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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  fs/userfaultfd.c
  *
  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
  *  Copyright (C) 2008-2009 Red Hat, Inc.
  *  Copyright (C) 2015  Red Hat, Inc.
  *
  *  Some part derived from fs/eventfd.c (anon inode setup) and
  *  mm/ksm.c (mm hashing).
  */
 
 #include <linux/list.h>
 #include <linux/hashtable.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/mm.h>
 #include <linux/mm.h>
 #include <linux/mm_inline.h>
 #include <linux/mmu_notifier.h>
 #include <linux/poll.h>
 #include <linux/slab.h>
 #include <linux/seq_file.h>
 #include <linux/file.h>
 #include <linux/bug.h>
 #include <linux/anon_inodes.h>
 #include <linux/syscalls.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/mempolicy.h>
 #include <linux/ioctl.h>
 #include <linux/security.h>
 #include <linux/hugetlb.h>
 #include <linux/swapops.h>
 
 int sysctl_unprivileged_userfaultfd __read_mostly;
 
 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
 
 /*
  * Start with fault_pending_wqh and fault_wqh so they're more likely
  * to be in the same cacheline.
  *
  * Locking order:
  *  fd_wqh.lock
  *      fault_pending_wqh.lock
  *          fault_wqh.lock
  *      event_wqh.lock
  *
  * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
  * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
  * also taken in IRQ context.
  */
 struct userfaultfd_ctx {
     /* waitqueue head for the pending (i.e. not read) userfaults */
     wait_queue_head_t fault_pending_wqh;
     /* waitqueue head for the userfaults */
     wait_queue_head_t fault_wqh;
     /* waitqueue head for the pseudo fd to wakeup poll/read */
     wait_queue_head_t fd_wqh;
     /* waitqueue head for events */
     wait_queue_head_t event_wqh;
     /* a refile sequence protected by fault_pending_wqh lock */
     seqcount_spinlock_t refile_seq;
     /* pseudo fd refcounting */
     refcount_t refcount;
     /* userfaultfd syscall flags */
     unsigned int flags;
     /* features requested from the userspace */
     unsigned int features;
     /* released */
     bool released;
     /* memory mappings are changing because of non-cooperative event */
     atomic_t mmap_changing;
     /* mm with one ore more vmas attached to this userfaultfd_ctx */
     struct mm_struct *mm;
 };
 
 struct userfaultfd_fork_ctx {
     struct userfaultfd_ctx *orig;
     struct userfaultfd_ctx *new;
     struct list_head list;
 };
 
 struct userfaultfd_unmap_ctx {
     struct userfaultfd_ctx *ctx;
     unsigned long start;
     unsigned long end;
     struct list_head list;
 };
 
 struct userfaultfd_wait_queue {
     struct uffd_msg msg;
     wait_queue_entry_t wq;
     struct userfaultfd_ctx *ctx;
     bool waken;
 };
 
 struct userfaultfd_wake_range {
     unsigned long start;
     unsigned long len;
 };
 
 /* internal indication that UFFD_API ioctl was successfully executed */
 #define UFFD_FEATURE_INITIALIZED        (1u << 31)
 
 static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
 {
     return ctx->features & UFFD_FEATURE_INITIALIZED;
 }
 
 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
                      int wake_flags, void *key)
 {
     struct userfaultfd_wake_range *range = key;
     int ret;
     struct userfaultfd_wait_queue *uwq;
     unsigned long start, len;
 
     uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
     ret = 0;
     /* len == 0 means wake all */
     start = range->start;
     len = range->len;
     if (len && (start > uwq->msg.arg.pagefault.address ||
             start + len <= uwq->msg.arg.pagefault.address))
         goto out;
     WRITE_ONCE(uwq->waken, true);
     /*
      * The Program-Order guarantees provided by the scheduler
      * ensure uwq->waken is visible before the task is woken.
      */
     ret = wake_up_state(wq->private, mode);
     if (ret) {
         /*
          * Wake only once, autoremove behavior.
          *
          * After the effect of list_del_init is visible to the other
          * CPUs, the waitqueue may disappear from under us, see the
          * !list_empty_careful() in handle_userfault().
          *
          * try_to_wake_up() has an implicit smp_mb(), and the
          * wq->private is read before calling the extern function
          * "wake_up_state" (which in turns calls try_to_wake_up).
          */
         list_del_init(&wq->entry);
     }
 out:
     return ret;
 }
 
 /**
  * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
  * context.
  * @ctx: [in] Pointer to the userfaultfd context.
  */
 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
 {
     refcount_inc(&ctx->refcount);
 }
 
 /**
  * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
  * context.
  * @ctx: [in] Pointer to userfaultfd context.
  *
  * The userfaultfd context reference must have been previously acquired either
  * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
  */
 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
 {
     if (refcount_dec_and_test(&ctx->refcount)) {
         VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
         VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
         VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
         VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
         VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
         VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
         VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
         VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
         mmdrop(ctx->mm);
         kmem_cache_free(userfaultfd_ctx_cachep, ctx);
     }
 }
 
 static inline void msg_init(struct uffd_msg *msg)
 {
     BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
     /*
      * Must use memset to zero out the paddings or kernel data is
      * leaked to userland.
      */
     memset(msg, 0, sizeof(struct uffd_msg));
 }
 
 static inline struct uffd_msg userfault_msg(unsigned long address,
                         unsigned long real_address,
                         unsigned int flags,
                         unsigned long reason,
                         unsigned int features)
 {
     struct uffd_msg msg;
 
     msg_init(&msg);
     msg.event = UFFD_EVENT_PAGEFAULT;
 
     msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
                     real_address : address;
 
     /*
      * These flags indicate why the userfault occurred:
      * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
      * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
      * - Neither of these flags being set indicates a MISSING fault.
      *
      * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
      * fault. Otherwise, it was a read fault.
      */
     if (flags & FAULT_FLAG_WRITE)
         msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
     if (reason & VM_UFFD_WP)
         msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
     if (reason & VM_UFFD_MINOR)
         msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
     if (features & UFFD_FEATURE_THREAD_ID)
         msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
     return msg;
 }
 
 #ifdef CONFIG_HUGETLB_PAGE
 /*
  * Same functionality as userfaultfd_must_wait below with modifications for
  * hugepmd ranges.
  */
 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
                      struct vm_area_struct *vma,
                      unsigned long address,
                      unsigned long flags,
                      unsigned long reason)
 {
     struct mm_struct *mm = ctx->mm;
     pte_t *ptep, pte;
     bool ret = true;
 
     mmap_assert_locked(mm);
 
     ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
 
     if (!ptep)
         goto out;
 
     ret = false;
     pte = huge_ptep_get(ptep);
 
     /*
      * Lockless access: we're in a wait_event so it's ok if it
      * changes under us.  PTE markers should be handled the same as none
      * ptes here.
      */
     if (huge_pte_none_mostly(pte))
         ret = true;
     if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
         ret = true;
 out:
     return ret;
 }
 #else
 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
                      struct vm_area_struct *vma,
                      unsigned long address,
                      unsigned long flags,
                      unsigned long reason)
 {
     return false;   /* should never get here */
 }
 #endif /* CONFIG_HUGETLB_PAGE */
 
 /*
  * Verify the pagetables are still not ok after having reigstered into
  * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
  * userfault that has already been resolved, if userfaultfd_read and
  * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
  * threads.
  */
 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
                      unsigned long address,
                      unsigned long flags,
                      unsigned long reason)
 {
     struct mm_struct *mm = ctx->mm;
     pgd_t *pgd;
     p4d_t *p4d;
     pud_t *pud;
     pmd_t *pmd, _pmd;
     pte_t *pte;
     bool ret = true;
 
     mmap_assert_locked(mm);
 
     pgd = pgd_offset(mm, address);
     if (!pgd_present(*pgd))
         goto out;
     p4d = p4d_offset(pgd, address);
     if (!p4d_present(*p4d))
         goto out;
     pud = pud_offset(p4d, address);
     if (!pud_present(*pud))
         goto out;
     pmd = pmd_offset(pud, address);
     /*
      * READ_ONCE must function as a barrier with narrower scope
      * and it must be equivalent to:
      *  _pmd = *pmd; barrier();
      *
      * This is to deal with the instability (as in
      * pmd_trans_unstable) of the pmd.
      */
     _pmd = READ_ONCE(*pmd);
     if (pmd_none(_pmd))
         goto out;
 
     ret = false;
     if (!pmd_present(_pmd))
         goto out;
 
     if (pmd_trans_huge(_pmd)) {
         if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
             ret = true;
         goto out;
     }
 
     /*
      * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
      * and use the standard pte_offset_map() instead of parsing _pmd.
      */
     pte = pte_offset_map(pmd, address);
     /*
      * Lockless access: we're in a wait_event so it's ok if it
      * changes under us.  PTE markers should be handled the same as none
      * ptes here.
      */
     if (pte_none_mostly(*pte))
         ret = true;
     if (!pte_write(*pte) && (reason & VM_UFFD_WP))
         ret = true;
     pte_unmap(pte);
 
 out:
     return ret;
 }
 
 static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
 {
     if (flags & FAULT_FLAG_INTERRUPTIBLE)
         return TASK_INTERRUPTIBLE;
 
     if (flags & FAULT_FLAG_KILLABLE)
         return TASK_KILLABLE;
 
     return TASK_UNINTERRUPTIBLE;
 }
 
 /*
  * The locking rules involved in returning VM_FAULT_RETRY depending on
  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
  * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
  * recommendation in __lock_page_or_retry is not an understatement.
  *
  * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
  * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
  * not set.
  *
  * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
  * set, VM_FAULT_RETRY can still be returned if and only if there are
  * fatal_signal_pending()s, and the mmap_lock must be released before
  * returning it.
  */
 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 {
     struct mm_struct *mm = vmf->vma->vm_mm;
     struct userfaultfd_ctx *ctx;
     struct userfaultfd_wait_queue uwq;
     vm_fault_t ret = VM_FAULT_SIGBUS;
     bool must_wait;
     unsigned int blocking_state;
 
     /*
      * We don't do userfault handling for the final child pid update.
      *
      * We also don't do userfault handling during
      * coredumping. hugetlbfs has the special
      * follow_hugetlb_page() to skip missing pages in the
      * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
      * the no_page_table() helper in follow_page_mask(), but the
      * shmem_vm_ops->fault method is invoked even during
      * coredumping without mmap_lock and it ends up here.
      */
     if (current->flags & (PF_EXITING|PF_DUMPCORE))
         goto out;
 
     /*
      * Coredumping runs without mmap_lock so we can only check that
      * the mmap_lock is held, if PF_DUMPCORE was not set.
      */
     mmap_assert_locked(mm);
 
     ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
     if (!ctx)
         goto out;
 
     BUG_ON(ctx->mm != mm);
 
     /* Any unrecognized flag is a bug. */
     VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
     /* 0 or > 1 flags set is a bug; we expect exactly 1. */
     VM_BUG_ON(!reason || (reason & (reason - 1)));
 
     if (ctx->features & UFFD_FEATURE_SIGBUS)
         goto out;
     if ((vmf->flags & FAULT_FLAG_USER) == 0 &&
         ctx->flags & UFFD_USER_MODE_ONLY) {
         printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
             "sysctl knob to 1 if kernel faults must be handled "
             "without obtaining CAP_SYS_PTRACE capability\n");
         goto out;
     }
 
     /*
      * If it's already released don't get it. This avoids to loop
      * in __get_user_pages if userfaultfd_release waits on the
      * caller of handle_userfault to release the mmap_lock.
      */
     if (unlikely(READ_ONCE(ctx->released))) {
         /*
          * Don't return VM_FAULT_SIGBUS in this case, so a non
          * cooperative manager can close the uffd after the
          * last UFFDIO_COPY, without risking to trigger an
          * involuntary SIGBUS if the process was starting the
          * userfaultfd while the userfaultfd was still armed
          * (but after the last UFFDIO_COPY). If the uffd
          * wasn't already closed when the userfault reached
          * this point, that would normally be solved by
          * userfaultfd_must_wait returning 'false'.
          *
          * If we were to return VM_FAULT_SIGBUS here, the non
          * cooperative manager would be instead forced to
          * always call UFFDIO_UNREGISTER before it can safely
          * close the uffd.
          */
         ret = VM_FAULT_NOPAGE;
         goto out;
     }
 
     /*
      * Check that we can return VM_FAULT_RETRY.
      *
      * NOTE: it should become possible to return VM_FAULT_RETRY
      * even if FAULT_FLAG_TRIED is set without leading to gup()
      * -EBUSY failures, if the userfaultfd is to be extended for
      * VM_UFFD_WP tracking and we intend to arm the userfault
      * without first stopping userland access to the memory. For
      * VM_UFFD_MISSING userfaults this is enough for now.
      */
     if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
         /*
          * Validate the invariant that nowait must allow retry
          * to be sure not to return SIGBUS erroneously on
          * nowait invocations.
          */
         BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
 #ifdef CONFIG_DEBUG_VM
         if (printk_ratelimit()) {
             printk(KERN_WARNING
                    "FAULT_FLAG_ALLOW_RETRY missing %x\n",
                    vmf->flags);
             dump_stack();
         }
 #endif
         goto out;
     }
 
     /*
      * Handle nowait, not much to do other than tell it to retry
      * and wait.
      */
     ret = VM_FAULT_RETRY;
     if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
         goto out;
 
     /* take the reference before dropping the mmap_lock */
     userfaultfd_ctx_get(ctx);
 
     init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
     uwq.wq.private = current;
     uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
                 reason, ctx->features);
     uwq.ctx = ctx;
     uwq.waken = false;
 
     blocking_state = userfaultfd_get_blocking_state(vmf->flags);
 
     spin_lock_irq(&ctx->fault_pending_wqh.lock);
     /*
      * After the __add_wait_queue the uwq is visible to userland
      * through poll/read().
      */
     __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
     /*
      * The smp_mb() after __set_current_state prevents the reads
      * following the spin_unlock to happen before the list_add in
      * __add_wait_queue.
      */
     set_current_state(blocking_state);
     spin_unlock_irq(&ctx->fault_pending_wqh.lock);
 
     if (!is_vm_hugetlb_page(vmf->vma))
         must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
                           reason);
     else
         must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
                                vmf->address,
                                vmf->flags, reason);
     mmap_read_unlock(mm);
 
     if (likely(must_wait && !READ_ONCE(ctx->released))) {
         wake_up_poll(&ctx->fd_wqh, EPOLLIN);
         schedule();
     }
 
     __set_current_state(TASK_RUNNING);
 
     /*
      * Here we race with the list_del; list_add in
      * userfaultfd_ctx_read(), however because we don't ever run
      * list_del_init() to refile across the two lists, the prev
      * and next pointers will never point to self. list_add also
      * would never let any of the two pointers to point to
      * self. So list_empty_careful won't risk to see both pointers
      * pointing to self at any time during the list refile. The
      * only case where list_del_init() is called is the full
      * removal in the wake function and there we don't re-list_add
      * and it's fine not to block on the spinlock. The uwq on this
      * kernel stack can be released after the list_del_init.
      */
     if (!list_empty_careful(&uwq.wq.entry)) {
         spin_lock_irq(&ctx->fault_pending_wqh.lock);
         /*
          * No need of list_del_init(), the uwq on the stack
          * will be freed shortly anyway.
          */
         list_del(&uwq.wq.entry);
         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
     }
 
     /*
      * ctx may go away after this if the userfault pseudo fd is
      * already released.
      */
     userfaultfd_ctx_put(ctx);
 
 out:
     return ret;
 }
 
 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
                           struct userfaultfd_wait_queue *ewq)
 {
     struct userfaultfd_ctx *release_new_ctx;
 
     if (WARN_ON_ONCE(current->flags & PF_EXITING))
         goto out;
 
     ewq->ctx = ctx;
     init_waitqueue_entry(&ewq->wq, current);
     release_new_ctx = NULL;
 
     spin_lock_irq(&ctx->event_wqh.lock);
     /*
      * After the __add_wait_queue the uwq is visible to userland
      * through poll/read().
      */
     __add_wait_queue(&ctx->event_wqh, &ewq->wq);
     for (;;) {
         set_current_state(TASK_KILLABLE);
         if (ewq->msg.event == 0)
             break;
         if (READ_ONCE(ctx->released) ||
             fatal_signal_pending(current)) {
             /*
              * &ewq->wq may be queued in fork_event, but
              * __remove_wait_queue ignores the head
              * parameter. It would be a problem if it
              * didn't.
              */
             __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
             if (ewq->msg.event == UFFD_EVENT_FORK) {
                 struct userfaultfd_ctx *new;
 
                 new = (struct userfaultfd_ctx *)
                     (unsigned long)
                     ewq->msg.arg.reserved.reserved1;
                 release_new_ctx = new;
             }
             break;
         }
 
         spin_unlock_irq(&ctx->event_wqh.lock);
 
         wake_up_poll(&ctx->fd_wqh, EPOLLIN);
         schedule();
 
         spin_lock_irq(&ctx->event_wqh.lock);
     }
     __set_current_state(TASK_RUNNING);
     spin_unlock_irq(&ctx->event_wqh.lock);
 
     if (release_new_ctx) {
         struct vm_area_struct *vma;
         struct mm_struct *mm = release_new_ctx->mm;
 
         /* the various vma->vm_userfaultfd_ctx still points to it */
         mmap_write_lock(mm);
         for (vma = mm->mmap; vma; vma = vma->vm_next)
             if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
                 vma->vm_flags &= ~__VM_UFFD_FLAGS;
             }
         mmap_write_unlock(mm);
 
         userfaultfd_ctx_put(release_new_ctx);
     }
 
     /*
      * ctx may go away after this if the userfault pseudo fd is
      * already released.
      */
 out:
     atomic_dec(&ctx->mmap_changing);
     VM_BUG_ON(atomic_read(&ctx->mmap_changing) < 0);
     userfaultfd_ctx_put(ctx);
 }
 
 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
                        struct userfaultfd_wait_queue *ewq)
 {
     ewq->msg.event = 0;
     wake_up_locked(&ctx->event_wqh);
     __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
 }
 
 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
 {
     struct userfaultfd_ctx *ctx = NULL, *octx;
     struct userfaultfd_fork_ctx *fctx;
 
     octx = vma->vm_userfaultfd_ctx.ctx;
     if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
         vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
         vma->vm_flags &= ~__VM_UFFD_FLAGS;
         return 0;
     }
 
     list_for_each_entry(fctx, fcs, list)
         if (fctx->orig == octx) {
             ctx = fctx->new;
             break;
         }
 
     if (!ctx) {
         fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
         if (!fctx)
             return -ENOMEM;
 
         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
         if (!ctx) {
             kfree(fctx);
             return -ENOMEM;
         }
 
         refcount_set(&ctx->refcount, 1);
         ctx->flags = octx->flags;
         ctx->features = octx->features;
         ctx->released = false;
         atomic_set(&ctx->mmap_changing, 0);
         ctx->mm = vma->vm_mm;
         mmgrab(ctx->mm);
 
         userfaultfd_ctx_get(octx);
         atomic_inc(&octx->mmap_changing);
         fctx->orig = octx;
         fctx->new = ctx;
         list_add_tail(&fctx->list, fcs);
     }
 
     vma->vm_userfaultfd_ctx.ctx = ctx;
     return 0;
 }
 
 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
 {
     struct userfaultfd_ctx *ctx = fctx->orig;
     struct userfaultfd_wait_queue ewq;
 
     msg_init(&ewq.msg);
 
     ewq.msg.event = UFFD_EVENT_FORK;
     ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
 
     userfaultfd_event_wait_completion(ctx, &ewq);
 }
 
 void dup_userfaultfd_complete(struct list_head *fcs)
 {
     struct userfaultfd_fork_ctx *fctx, *n;
 
     list_for_each_entry_safe(fctx, n, fcs, list) {
         dup_fctx(fctx);
         list_del(&fctx->list);
         kfree(fctx);
     }
 }
 
 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
                  struct vm_userfaultfd_ctx *vm_ctx)
 {
     struct userfaultfd_ctx *ctx;
 
     ctx = vma->vm_userfaultfd_ctx.ctx;
 
     if (!ctx)
         return;
 
     if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
         vm_ctx->ctx = ctx;
         userfaultfd_ctx_get(ctx);
         atomic_inc(&ctx->mmap_changing);
     } else {
         /* Drop uffd context if remap feature not enabled */
         vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
         vma->vm_flags &= ~__VM_UFFD_FLAGS;
     }
 }
 
 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
                  unsigned long from, unsigned long to,
                  unsigned long len)
 {
     struct userfaultfd_ctx *ctx = vm_ctx->ctx;
     struct userfaultfd_wait_queue ewq;
 
     if (!ctx)
         return;
 
     if (to & ~PAGE_MASK) {
         userfaultfd_ctx_put(ctx);
         return;
     }
 
     msg_init(&ewq.msg);
 
     ewq.msg.event = UFFD_EVENT_REMAP;
     ewq.msg.arg.remap.from = from;
     ewq.msg.arg.remap.to = to;
     ewq.msg.arg.remap.len = len;
 
     userfaultfd_event_wait_completion(ctx, &ewq);
 }
 
 bool userfaultfd_remove(struct vm_area_struct *vma,
             unsigned long start, unsigned long end)
 {
     struct mm_struct *mm = vma->vm_mm;
     struct userfaultfd_ctx *ctx;
     struct userfaultfd_wait_queue ewq;
 
     ctx = vma->vm_userfaultfd_ctx.ctx;
     if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
         return true;
 
     userfaultfd_ctx_get(ctx);
     atomic_inc(&ctx->mmap_changing);
     mmap_read_unlock(mm);
 
     msg_init(&ewq.msg);
 
     ewq.msg.event = UFFD_EVENT_REMOVE;
     ewq.msg.arg.remove.start = start;
     ewq.msg.arg.remove.end = end;
 
     userfaultfd_event_wait_completion(ctx, &ewq);
 
     return false;
 }
 
 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
               unsigned long start, unsigned long end)
 {
     struct userfaultfd_unmap_ctx *unmap_ctx;
 
     list_for_each_entry(unmap_ctx, unmaps, list)
         if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
             unmap_ctx->end == end)
             return true;
 
     return false;
 }
 
 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
                unsigned long start, unsigned long end,
                struct list_head *unmaps)
 {
     for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
         struct userfaultfd_unmap_ctx *unmap_ctx;
         struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
 
         if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
             has_unmap_ctx(ctx, unmaps, start, end))
             continue;
 
         unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
         if (!unmap_ctx)
             return -ENOMEM;
 
         userfaultfd_ctx_get(ctx);
         atomic_inc(&ctx->mmap_changing);
         unmap_ctx->ctx = ctx;
         unmap_ctx->start = start;
         unmap_ctx->end = end;
         list_add_tail(&unmap_ctx->list, unmaps);
     }
 
     return 0;
 }
 
 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
 {
     struct userfaultfd_unmap_ctx *ctx, *n;
     struct userfaultfd_wait_queue ewq;
 
     list_for_each_entry_safe(ctx, n, uf, list) {
         msg_init(&ewq.msg);
 
         ewq.msg.event = UFFD_EVENT_UNMAP;
         ewq.msg.arg.remove.start = ctx->start;
         ewq.msg.arg.remove.end = ctx->end;
 
         userfaultfd_event_wait_completion(ctx->ctx, &ewq);
 
         list_del(&ctx->list);
         kfree(ctx);
     }
 }
 
 static int userfaultfd_release(struct inode *inode, struct file *file)
 {
     struct userfaultfd_ctx *ctx = file->private_data;
     struct mm_struct *mm = ctx->mm;
     struct vm_area_struct *vma, *prev;
     /* len == 0 means wake all */
     struct userfaultfd_wake_range range = { .len = 0, };
     unsigned long new_flags;
 
     WRITE_ONCE(ctx->released, true);
 
     if (!mmget_not_zero(mm))
         goto wakeup;
 
     /*
      * Flush page faults out of all CPUs. NOTE: all page faults
      * must be retried without returning VM_FAULT_SIGBUS if
      * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
      * changes while handle_userfault released the mmap_lock. So
      * it's critical that released is set to true (above), before
      * taking the mmap_lock for writing.
      */
     mmap_write_lock(mm);
     prev = NULL;
     for (vma = mm->mmap; vma; vma = vma->vm_next) {
         cond_resched();
         BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
                !!(vma->vm_flags & __VM_UFFD_FLAGS));
         if (vma->vm_userfaultfd_ctx.ctx != ctx) {
             prev = vma;
             continue;
         }
         new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
         prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
                  new_flags, vma->anon_vma,
                  vma->vm_file, vma->vm_pgoff,
                  vma_policy(vma),
                  NULL_VM_UFFD_CTX, anon_vma_name(vma));
         if (prev)
             vma = prev;
         else
             prev = vma;
         vma->vm_flags = new_flags;
         vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
     }
     mmap_write_unlock(mm);
     mmput(mm);
 wakeup:
     /*
      * After no new page faults can wait on this fault_*wqh, flush
      * the last page faults that may have been already waiting on
      * the fault_*wqh.
      */
     spin_lock_irq(&ctx->fault_pending_wqh.lock);
     __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
     __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
     spin_unlock_irq(&ctx->fault_pending_wqh.lock);
 
     /* Flush pending events that may still wait on event_wqh */
     wake_up_all(&ctx->event_wqh);
 
     wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
     userfaultfd_ctx_put(ctx);
     return 0;
 }
 
 /* fault_pending_wqh.lock must be hold by the caller */
 static inline struct userfaultfd_wait_queue *find_userfault_in(
         wait_queue_head_t *wqh)
 {
     wait_queue_entry_t *wq;
     struct userfaultfd_wait_queue *uwq;
 
     lockdep_assert_held(&wqh->lock);
 
     uwq = NULL;
     if (!waitqueue_active(wqh))
         goto out;
     /* walk in reverse to provide FIFO behavior to read userfaults */
     wq = list_last_entry(&wqh->head, typeof(*wq), entry);
     uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
 out:
     return uwq;
 }
 
 static inline struct userfaultfd_wait_queue *find_userfault(
         struct userfaultfd_ctx *ctx)
 {
     return find_userfault_in(&ctx->fault_pending_wqh);
 }
 
 static inline struct userfaultfd_wait_queue *find_userfault_evt(
         struct userfaultfd_ctx *ctx)
 {
     return find_userfault_in(&ctx->event_wqh);
 }
 
 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
 {
     struct userfaultfd_ctx *ctx = file->private_data;
     __poll_t ret;
 
     poll_wait(file, &ctx->fd_wqh, wait);
 
     if (!userfaultfd_is_initialized(ctx))
         return EPOLLERR;
 
     /*
      * poll() never guarantees that read won't block.
      * userfaults can be waken before they're read().
      */
     if (unlikely(!(file->f_flags & O_NONBLOCK)))
         return EPOLLERR;
     /*
      * lockless access to see if there are pending faults
      * __pollwait last action is the add_wait_queue but
      * the spin_unlock would allow the waitqueue_active to
      * pass above the actual list_add inside
      * add_wait_queue critical section. So use a full
      * memory barrier to serialize the list_add write of
      * add_wait_queue() with the waitqueue_active read
      * below.
      */
     ret = 0;
     smp_mb();
     if (waitqueue_active(&ctx->fault_pending_wqh))
         ret = EPOLLIN;
     else if (waitqueue_active(&ctx->event_wqh))
         ret = EPOLLIN;
 
     return ret;
 }
 
 static const struct file_operations userfaultfd_fops;
 
 static int resolve_userfault_fork(struct userfaultfd_ctx *new,
                   struct inode *inode,
                   struct uffd_msg *msg)
 {
     int fd;
 
     fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
             O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
     if (fd < 0)
         return fd;
 
     msg->arg.reserved.reserved1 = 0;
     msg->arg.fork.ufd = fd;
     return 0;
 }
 
 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
                     struct uffd_msg *msg, struct inode *inode)
 {
     ssize_t ret;
     DECLARE_WAITQUEUE(wait, current);
     struct userfaultfd_wait_queue *uwq;
     /*
      * Handling fork event requires sleeping operations, so
      * we drop the event_wqh lock, then do these ops, then
      * lock it back and wake up the waiter. While the lock is
      * dropped the ewq may go away so we keep track of it
      * carefully.
      */
     LIST_HEAD(fork_event);
     struct userfaultfd_ctx *fork_nctx = NULL;
 
     /* always take the fd_wqh lock before the fault_pending_wqh lock */
     spin_lock_irq(&ctx->fd_wqh.lock);
     __add_wait_queue(&ctx->fd_wqh, &wait);
     for (;;) {
         set_current_state(TASK_INTERRUPTIBLE);
         spin_lock(&ctx->fault_pending_wqh.lock);
         uwq = find_userfault(ctx);
         if (uwq) {
             /*
              * Use a seqcount to repeat the lockless check
              * in wake_userfault() to avoid missing
              * wakeups because during the refile both
              * waitqueue could become empty if this is the
              * only userfault.
              */
             write_seqcount_begin(&ctx->refile_seq);
 
             /*
              * The fault_pending_wqh.lock prevents the uwq
              * to disappear from under us.
              *
              * Refile this userfault from
              * fault_pending_wqh to fault_wqh, it's not
              * pending anymore after we read it.
              *
              * Use list_del() by hand (as
              * userfaultfd_wake_function also uses
              * list_del_init() by hand) to be sure nobody
              * changes __remove_wait_queue() to use
              * list_del_init() in turn breaking the
              * !list_empty_careful() check in
              * handle_userfault(). The uwq->wq.head list
              * must never be empty at any time during the
              * refile, or the waitqueue could disappear
              * from under us. The "wait_queue_head_t"
              * parameter of __remove_wait_queue() is unused
              * anyway.
              */
             list_del(&uwq->wq.entry);
             add_wait_queue(&ctx->fault_wqh, &uwq->wq);
 
             write_seqcount_end(&ctx->refile_seq);
 
             /* careful to always initialize msg if ret == 0 */
             *msg = uwq->msg;
             spin_unlock(&ctx->fault_pending_wqh.lock);
             ret = 0;
             break;
         }
         spin_unlock(&ctx->fault_pending_wqh.lock);
 
         spin_lock(&ctx->event_wqh.lock);
         uwq = find_userfault_evt(ctx);
         if (uwq) {
             *msg = uwq->msg;
 
             if (uwq->msg.event == UFFD_EVENT_FORK) {
                 fork_nctx = (struct userfaultfd_ctx *)
                     (unsigned long)
                     uwq->msg.arg.reserved.reserved1;
                 list_move(&uwq->wq.entry, &fork_event);
                 /*
                  * fork_nctx can be freed as soon as
                  * we drop the lock, unless we take a
                  * reference on it.
                  */
                 userfaultfd_ctx_get(fork_nctx);
                 spin_unlock(&ctx->event_wqh.lock);
                 ret = 0;
                 break;
             }
 
             userfaultfd_event_complete(ctx, uwq);
             spin_unlock(&ctx->event_wqh.lock);
             ret = 0;
             break;
         }
         spin_unlock(&ctx->event_wqh.lock);
 
         if (signal_pending(current)) {
             ret = -ERESTARTSYS;
             break;
         }
         if (no_wait) {
             ret = -EAGAIN;
             break;
         }
         spin_unlock_irq(&ctx->fd_wqh.lock);
         schedule();
         spin_lock_irq(&ctx->fd_wqh.lock);
     }
     __remove_wait_queue(&ctx->fd_wqh, &wait);
     __set_current_state(TASK_RUNNING);
     spin_unlock_irq(&ctx->fd_wqh.lock);
 
     if (!ret && msg->event == UFFD_EVENT_FORK) {
         ret = resolve_userfault_fork(fork_nctx, inode, msg);
         spin_lock_irq(&ctx->event_wqh.lock);
         if (!list_empty(&fork_event)) {
             /*
              * The fork thread didn't abort, so we can
              * drop the temporary refcount.
              */
             userfaultfd_ctx_put(fork_nctx);
 
             uwq = list_first_entry(&fork_event,
                            typeof(*uwq),
                            wq.entry);
             /*
              * If fork_event list wasn't empty and in turn
              * the event wasn't already released by fork
              * (the event is allocated on fork kernel
              * stack), put the event back to its place in
              * the event_wq. fork_event head will be freed
              * as soon as we return so the event cannot
              * stay queued there no matter the current
              * "ret" value.
              */
             list_del(&uwq->wq.entry);
             __add_wait_queue(&ctx->event_wqh, &uwq->wq);
 
             /*
              * Leave the event in the waitqueue and report
              * error to userland if we failed to resolve
              * the userfault fork.
              */
             if (likely(!ret))
                 userfaultfd_event_complete(ctx, uwq);
         } else {
             /*
              * Here the fork thread aborted and the
              * refcount from the fork thread on fork_nctx
              * has already been released. We still hold
              * the reference we took before releasing the
              * lock above. If resolve_userfault_fork
              * failed we've to drop it because the
              * fork_nctx has to be freed in such case. If
              * it succeeded we'll hold it because the new
              * uffd references it.
              */
             if (ret)
                 userfaultfd_ctx_put(fork_nctx);
         }
         spin_unlock_irq(&ctx->event_wqh.lock);
     }
 
     return ret;
 }
 
 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
                 size_t count, loff_t *ppos)
 {
     struct userfaultfd_ctx *ctx = file->private_data;
     ssize_t _ret, ret = 0;
     struct uffd_msg msg;
     int no_wait = file->f_flags & O_NONBLOCK;
     struct inode *inode = file_inode(file);
 
     if (!userfaultfd_is_initialized(ctx))
         return -EINVAL;
 
     for (;;) {
         if (count < sizeof(msg))
             return ret ? ret : -EINVAL;
         _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
         if (_ret < 0)
             return ret ? ret : _ret;
         if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
             return ret ? ret : -EFAULT;
         ret += sizeof(msg);
         buf += sizeof(msg);
         count -= sizeof(msg);
         /*
          * Allow to read more than one fault at time but only
          * block if waiting for the very first one.
          */
         no_wait = O_NONBLOCK;
     }
 }
 
 static void __wake_userfault(struct userfaultfd_ctx *ctx,
                  struct userfaultfd_wake_range *range)
 {
     spin_lock_irq(&ctx->fault_pending_wqh.lock);
     /* wake all in the range and autoremove */
     if (waitqueue_active(&ctx->fault_pending_wqh))
         __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
                      range);
     if (waitqueue_active(&ctx->fault_wqh))
         __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
     spin_unlock_irq(&ctx->fault_pending_wqh.lock);
 }
 
 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
                        struct userfaultfd_wake_range *range)
 {
     unsigned seq;
     bool need_wakeup;
 
     /*
      * To be sure waitqueue_active() is not reordered by the CPU
      * before the pagetable update, use an explicit SMP memory
      * barrier here. PT lock release or mmap_read_unlock(mm) still
      * have release semantics that can allow the
      * waitqueue_active() to be reordered before the pte update.
      */
     smp_mb();
 
     /*
      * Use waitqueue_active because it's very frequent to
      * change the address space atomically even if there are no
      * userfaults yet. So we take the spinlock only when we're
      * sure we've userfaults to wake.
      */
     do {
         seq = read_seqcount_begin(&ctx->refile_seq);
         need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
             waitqueue_active(&ctx->fault_wqh);
         cond_resched();
     } while (read_seqcount_retry(&ctx->refile_seq, seq));
     if (need_wakeup)
         __wake_userfault(ctx, range);
 }
 
 static __always_inline int validate_range(struct mm_struct *mm,
                       __u64 start, __u64 len)
 {
     __u64 task_size = mm->task_size;
 
     if (start & ~PAGE_MASK)
         return -EINVAL;
     if (len & ~PAGE_MASK)
         return -EINVAL;
     if (!len)
         return -EINVAL;
     if (start < mmap_min_addr)
         return -EINVAL;
     if (start >= task_size)
         return -EINVAL;
     if (len > task_size - start)
         return -EINVAL;
     return 0;
 }
 
 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
                 unsigned long arg)
 {
     struct mm_struct *mm = ctx->mm;
     struct vm_area_struct *vma, *prev, *cur;
     int ret;
     struct uffdio_register uffdio_register;
     struct uffdio_register __user *user_uffdio_register;
     unsigned long vm_flags, new_flags;
     bool found;
     bool basic_ioctls;
     unsigned long start, end, vma_end;
 
     user_uffdio_register = (struct uffdio_register __user *) arg;
 
     ret = -EFAULT;
     if (copy_from_user(&uffdio_register, user_uffdio_register,
                sizeof(uffdio_register)-sizeof(__u64)))
         goto out;
 
     ret = -EINVAL;
     if (!uffdio_register.mode)
         goto out;
     if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
         goto out;
     vm_flags = 0;
     if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
         vm_flags |= VM_UFFD_MISSING;
     if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
         goto out;
 #endif
         vm_flags |= VM_UFFD_WP;
     }
     if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
         goto out;
 #endif
         vm_flags |= VM_UFFD_MINOR;
     }
 
     ret = validate_range(mm, uffdio_register.range.start,
                  uffdio_register.range.len);
     if (ret)
         goto out;
 
     start = uffdio_register.range.start;
     end = start + uffdio_register.range.len;
 
     ret = -ENOMEM;
     if (!mmget_not_zero(mm))
         goto out;
 
     mmap_write_lock(mm);
     vma = find_vma_prev(mm, start, &prev);
     if (!vma)
         goto out_unlock;
 
     /* check that there's at least one vma in the range */
     ret = -EINVAL;
     if (vma->vm_start >= end)
         goto out_unlock;
 
     /*
      * If the first vma contains huge pages, make sure start address
      * is aligned to huge page size.
      */
     if (is_vm_hugetlb_page(vma)) {
         unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
 
         if (start & (vma_hpagesize - 1))
             goto out_unlock;
     }
 
     /*
      * Search for not compatible vmas.
      */
     found = false;
     basic_ioctls = false;
     for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
         cond_resched();
 
         BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
                !!(cur->vm_flags & __VM_UFFD_FLAGS));
 
         /* check not compatible vmas */
         ret = -EINVAL;
         if (!vma_can_userfault(cur, vm_flags))
             goto out_unlock;
 
         /*
          * UFFDIO_COPY will fill file holes even without
          * PROT_WRITE. This check enforces that if this is a
          * MAP_SHARED, the process has write permission to the backing
          * file. If VM_MAYWRITE is set it also enforces that on a
          * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
          * F_WRITE_SEAL can be taken until the vma is destroyed.
          */
         ret = -EPERM;
         if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
             goto out_unlock;
 
         /*
          * If this vma contains ending address, and huge pages
          * check alignment.
          */
         if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
             end > cur->vm_start) {
             unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
 
             ret = -EINVAL;
 
             if (end & (vma_hpagesize - 1))
                 goto out_unlock;
         }
         if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
             goto out_unlock;
 
         /*
          * Check that this vma isn't already owned by a
          * different userfaultfd. We can't allow more than one
          * userfaultfd to own a single vma simultaneously or we
          * wouldn't know which one to deliver the userfaults to.
          */
         ret = -EBUSY;
         if (cur->vm_userfaultfd_ctx.ctx &&
             cur->vm_userfaultfd_ctx.ctx != ctx)
             goto out_unlock;
 
         /*
          * Note vmas containing huge pages
          */
         if (is_vm_hugetlb_page(cur))
             basic_ioctls = true;
 
         found = true;
     }
     BUG_ON(!found);
 
     if (vma->vm_start < start)
         prev = vma;
 
     ret = 0;
     do {
         cond_resched();
 
         BUG_ON(!vma_can_userfault(vma, vm_flags));
         BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
                vma->vm_userfaultfd_ctx.ctx != ctx);
         WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
 
         /*
          * Nothing to do: this vma is already registered into this
          * userfaultfd and with the right tracking mode too.
          */
         if (vma->vm_userfaultfd_ctx.ctx == ctx &&
             (vma->vm_flags & vm_flags) == vm_flags)
             goto skip;
 
         if (vma->vm_start > start)
             start = vma->vm_start;
         vma_end = min(end, vma->vm_end);
 
         new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
         prev = vma_merge(mm, prev, start, vma_end, new_flags,
                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
                  vma_policy(vma),
                  ((struct vm_userfaultfd_ctx){ ctx }),
                  anon_vma_name(vma));
         if (prev) {
             vma = prev;
             goto next;
         }
         if (vma->vm_start < start) {
             ret = split_vma(mm, vma, start, 1);
             if (ret)
                 break;
         }
         if (vma->vm_end > end) {
             ret = split_vma(mm, vma, end, 0);
             if (ret)
                 break;
         }
     next:
         /*
          * In the vma_merge() successful mprotect-like case 8:
          * the next vma was merged into the current one and
          * the current one has not been updated yet.
          */
         vma->vm_flags = new_flags;
         vma->vm_userfaultfd_ctx.ctx = ctx;
 
         if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
             hugetlb_unshare_all_pmds(vma);
 
     skip:
         prev = vma;
         start = vma->vm_end;
         vma = vma->vm_next;
     } while (vma && vma->vm_start < end);
 out_unlock:
     mmap_write_unlock(mm);
     mmput(mm);
     if (!ret) {
         __u64 ioctls_out;
 
         ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
             UFFD_API_RANGE_IOCTLS;
 
         /*
          * Declare the WP ioctl only if the WP mode is
          * specified and all checks passed with the range
          */
         if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
             ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
 
         /* CONTINUE ioctl is only supported for MINOR ranges. */
         if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
             ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
 
         /*
          * Now that we scanned all vmas we can already tell
          * userland which ioctls methods are guaranteed to
          * succeed on this range.
          */
         if (put_user(ioctls_out, &user_uffdio_register->ioctls))
             ret = -EFAULT;
     }
 out:
     return ret;
 }
 
 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
                   unsigned long arg)
 {
     struct mm_struct *mm = ctx->mm;
     struct vm_area_struct *vma, *prev, *cur;
     int ret;
     struct uffdio_range uffdio_unregister;
     unsigned long new_flags;
     bool found;
     unsigned long start, end, vma_end;
     const void __user *buf = (void __user *)arg;
 
     ret = -EFAULT;
     if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
         goto out;
 
     ret = validate_range(mm, uffdio_unregister.start,
                  uffdio_unregister.len);
     if (ret)
         goto out;
 
     start = uffdio_unregister.start;
     end = start + uffdio_unregister.len;
 
     ret = -ENOMEM;
     if (!mmget_not_zero(mm))
         goto out;
 
     mmap_write_lock(mm);
     vma = find_vma_prev(mm, start, &prev);
     if (!vma)
         goto out_unlock;
 
     /* check that there's at least one vma in the range */
     ret = -EINVAL;
     if (vma->vm_start >= end)
         goto out_unlock;
 
     /*
      * If the first vma contains huge pages, make sure start address
      * is aligned to huge page size.
      */
     if (is_vm_hugetlb_page(vma)) {
         unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
 
         if (start & (vma_hpagesize - 1))
             goto out_unlock;
     }
 
     /*
      * Search for not compatible vmas.
      */
     found = false;
     ret = -EINVAL;
     for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
         cond_resched();
 
         BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
                !!(cur->vm_flags & __VM_UFFD_FLAGS));
 
         /*
          * Check not compatible vmas, not strictly required
          * here as not compatible vmas cannot have an
          * userfaultfd_ctx registered on them, but this
          * provides for more strict behavior to notice
          * unregistration errors.
          */
         if (!vma_can_userfault(cur, cur->vm_flags))
             goto out_unlock;
 
         found = true;
     }
     BUG_ON(!found);
 
     if (vma->vm_start < start)
         prev = vma;
 
     ret = 0;
     do {
         cond_resched();
 
         BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
 
         /*
          * Nothing to do: this vma is already registered into this
          * userfaultfd and with the right tracking mode too.
          */
         if (!vma->vm_userfaultfd_ctx.ctx)
             goto skip;
 
         WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
 
         if (vma->vm_start > start)
             start = vma->vm_start;
         vma_end = min(end, vma->vm_end);
 
         if (userfaultfd_missing(vma)) {
             /*
              * Wake any concurrent pending userfault while
              * we unregister, so they will not hang
              * permanently and it avoids userland to call
              * UFFDIO_WAKE explicitly.
              */
             struct userfaultfd_wake_range range;
             range.start = start;
             range.len = vma_end - start;
             wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
         }
 
         /* Reset ptes for the whole vma range if wr-protected */
         if (userfaultfd_wp(vma))
             uffd_wp_range(mm, vma, start, vma_end - start, false);
 
         new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
         prev = vma_merge(mm, prev, start, vma_end, new_flags,
                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
                  vma_policy(vma),
                  NULL_VM_UFFD_CTX, anon_vma_name(vma));
         if (prev) {
             vma = prev;
             goto next;
         }
         if (vma->vm_start < start) {
             ret = split_vma(mm, vma, start, 1);
             if (ret)
                 break;
         }
         if (vma->vm_end > end) {
             ret = split_vma(mm, vma, end, 0);
             if (ret)
                 break;
         }
     next:
         /*
          * In the vma_merge() successful mprotect-like case 8:
          * the next vma was merged into the current one and
          * the current one has not been updated yet.
          */
         vma->vm_flags = new_flags;
         vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
 
     skip:
         prev = vma;
         start = vma->vm_end;
         vma = vma->vm_next;
     } while (vma && vma->vm_start < end);
 out_unlock:
     mmap_write_unlock(mm);
     mmput(mm);
 out:
     return ret;
 }
 
 /*
  * userfaultfd_wake may be used in combination with the
  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
  */
 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
                 unsigned long arg)
 {
     int ret;
     struct uffdio_range uffdio_wake;
     struct userfaultfd_wake_range range;
     const void __user *buf = (void __user *)arg;
 
     ret = -EFAULT;
     if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
         goto out;
 
     ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
     if (ret)
         goto out;
 
     range.start = uffdio_wake.start;
     range.len = uffdio_wake.len;
 
     /*
      * len == 0 means wake all and we don't want to wake all here,
      * so check it again to be sure.
      */
     VM_BUG_ON(!range.len);
 
     wake_userfault(ctx, &range);
     ret = 0;
 
 out:
     return ret;
 }
 
 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
                 unsigned long arg)
 {
     __s64 ret;
     struct uffdio_copy uffdio_copy;
     struct uffdio_copy __user *user_uffdio_copy;
     struct userfaultfd_wake_range range;
 
     user_uffdio_copy = (struct uffdio_copy __user *) arg;
 
     ret = -EAGAIN;
     if (atomic_read(&ctx->mmap_changing))
         goto out;
 
     ret = -EFAULT;
     if (copy_from_user(&uffdio_copy, user_uffdio_copy,
                /* don't copy "copy" last field */
                sizeof(uffdio_copy)-sizeof(__s64)))
         goto out;
 
     ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
     if (ret)
         goto out;
     /*
      * double check for wraparound just in case. copy_from_user()
      * will later check uffdio_copy.src + uffdio_copy.len to fit
      * in the userland range.
      */
     ret = -EINVAL;
     if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
         goto out;
     if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
         goto out;
     if (mmget_not_zero(ctx->mm)) {
         ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
                    uffdio_copy.len, &ctx->mmap_changing,
                    uffdio_copy.mode);
         mmput(ctx->mm);
     } else {
         return -ESRCH;
     }
     if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
         return -EFAULT;
     if (ret < 0)
         goto out;
     BUG_ON(!ret);
     /* len == 0 would wake all */
     range.len = ret;
     if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
         range.start = uffdio_copy.dst;
         wake_userfault(ctx, &range);
     }
     ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
 out:
     return ret;
 }
 
 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
                 unsigned long arg)
 {
     __s64 ret;
     struct uffdio_zeropage uffdio_zeropage;
     struct uffdio_zeropage __user *user_uffdio_zeropage;
     struct userfaultfd_wake_range range;
 
     user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
 
     ret = -EAGAIN;
     if (atomic_read(&ctx->mmap_changing))
         goto out;
 
     ret = -EFAULT;
     if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
                /* don't copy "zeropage" last field */
                sizeof(uffdio_zeropage)-sizeof(__s64)))
         goto out;
 
     ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
                  uffdio_zeropage.range.len);
     if (ret)
         goto out;
     ret = -EINVAL;
     if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
         goto out;
 
     if (mmget_not_zero(ctx->mm)) {
         ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
                      uffdio_zeropage.range.len,
                      &ctx->mmap_changing);
         mmput(ctx->mm);
     } else {
         return -ESRCH;
     }
     if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
         return -EFAULT;
     if (ret < 0)
         goto out;
     /* len == 0 would wake all */
     BUG_ON(!ret);
     range.len = ret;
     if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
         range.start = uffdio_zeropage.range.start;
         wake_userfault(ctx, &range);
     }
     ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
 out:
     return ret;
 }
 
 static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
                     unsigned long arg)
 {
     int ret;
     struct uffdio_writeprotect uffdio_wp;
     struct uffdio_writeprotect __user *user_uffdio_wp;
     struct userfaultfd_wake_range range;
     bool mode_wp, mode_dontwake;
 
     if (atomic_read(&ctx->mmap_changing))
         return -EAGAIN;
 
     user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
 
     if (copy_from_user(&uffdio_wp, user_uffdio_wp,
                sizeof(struct uffdio_writeprotect)))
         return -EFAULT;
 
     ret = validate_range(ctx->mm, uffdio_wp.range.start,
                  uffdio_wp.range.len);
     if (ret)
         return ret;
 
     if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
                    UFFDIO_WRITEPROTECT_MODE_WP))
         return -EINVAL;
 
     mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
     mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
 
     if (mode_wp && mode_dontwake)
         return -EINVAL;
 
     if (mmget_not_zero(ctx->mm)) {
         ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
                       uffdio_wp.range.len, mode_wp,
                       &ctx->mmap_changing);
         mmput(ctx->mm);
     } else {
         return -ESRCH;
     }
 
     if (ret)
         return ret;
 
     if (!mode_wp && !mode_dontwake) {
         range.start = uffdio_wp.range.start;
         range.len = uffdio_wp.range.len;
         wake_userfault(ctx, &range);
     }
     return ret;
 }
 
 static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
 {
     __s64 ret;
     struct uffdio_continue uffdio_continue;
     struct uffdio_continue __user *user_uffdio_continue;
     struct userfaultfd_wake_range range;
 
     user_uffdio_continue = (struct uffdio_continue __user *)arg;
 
     ret = -EAGAIN;
     if (atomic_read(&ctx->mmap_changing))
         goto out;
 
     ret = -EFAULT;
     if (copy_from_user(&uffdio_continue, user_uffdio_continue,
                /* don't copy the output fields */
                sizeof(uffdio_continue) - (sizeof(__s64))))
         goto out;
 
     ret = validate_range(ctx->mm, uffdio_continue.range.start,
                  uffdio_continue.range.len);
     if (ret)
         goto out;
 
     ret = -EINVAL;
     /* double check for wraparound just in case. */
     if (uffdio_continue.range.start + uffdio_continue.range.len <=
         uffdio_continue.range.start) {
         goto out;
     }
     if (uffdio_continue.mode & ~UFFDIO_CONTINUE_MODE_DONTWAKE)
         goto out;
 
     if (mmget_not_zero(ctx->mm)) {
         ret = mcopy_continue(ctx->mm, uffdio_continue.range.start,
                      uffdio_continue.range.len,
                      &ctx->mmap_changing);
         mmput(ctx->mm);
     } else {
         return -ESRCH;
     }
 
     if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
         return -EFAULT;
     if (ret < 0)
         goto out;
 
     /* len == 0 would wake all */
     BUG_ON(!ret);
     range.len = ret;
     if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
         range.start = uffdio_continue.range.start;
         wake_userfault(ctx, &range);
     }
     ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
 
 out:
     return ret;
 }
 
 static inline unsigned int uffd_ctx_features(__u64 user_features)
 {
     /*
      * For the current set of features the bits just coincide. Set
      * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
      */
     return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
 }
 
 /*
  * userland asks for a certain API version and we return which bits
  * and ioctl commands are implemented in this kernel for such API
  * version or -EINVAL if unknown.
  */
 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
                unsigned long arg)
 {
     struct uffdio_api uffdio_api;
     void __user *buf = (void __user *)arg;
     unsigned int ctx_features;
     int ret;
     __u64 features;
 
     ret = -EFAULT;
     if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
         goto out;
     /* Ignore unsupported features (userspace built against newer kernel) */
     features = uffdio_api.features & UFFD_API_FEATURES;
     ret = -EPERM;
     if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
         goto err_out;
     /* report all available features and ioctls to userland */
     uffdio_api.features = UFFD_API_FEATURES;
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
     uffdio_api.features &=
         ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
 #endif
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
     uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
 #endif
 #ifndef CONFIG_PTE_MARKER_UFFD_WP
     uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
 #endif
     uffdio_api.ioctls = UFFD_API_IOCTLS;
     ret = -EFAULT;
     if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
         goto out;
 
     /* only enable the requested features for this uffd context */
     ctx_features = uffd_ctx_features(features);
     ret = -EINVAL;
     if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
         goto err_out;
 
     ret = 0;
 out:
     return ret;
 err_out:
     memset(&uffdio_api, 0, sizeof(uffdio_api));
     if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
         ret = -EFAULT;
     goto out;
 }
 
 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
                   unsigned long arg)
 {
     int ret = -EINVAL;
     struct userfaultfd_ctx *ctx = file->private_data;
 
     if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
         return -EINVAL;
 
     switch(cmd) {
     case UFFDIO_API:
         ret = userfaultfd_api(ctx, arg);
         break;
     case UFFDIO_REGISTER:
         ret = userfaultfd_register(ctx, arg);
         break;
     case UFFDIO_UNREGISTER:
         ret = userfaultfd_unregister(ctx, arg);
         break;
     case UFFDIO_WAKE:
         ret = userfaultfd_wake(ctx, arg);
         break;
     case UFFDIO_COPY:
         ret = userfaultfd_copy(ctx, arg);
         break;
     case UFFDIO_ZEROPAGE:
         ret = userfaultfd_zeropage(ctx, arg);
         break;
     case UFFDIO_WRITEPROTECT:
         ret = userfaultfd_writeprotect(ctx, arg);
         break;
     case UFFDIO_CONTINUE:
         ret = userfaultfd_continue(ctx, arg);
         break;
     }
     return ret;
 }
 
 #ifdef CONFIG_PROC_FS
 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
 {
     struct userfaultfd_ctx *ctx = f->private_data;
     wait_queue_entry_t *wq;
     unsigned long pending = 0, total = 0;
 
     spin_lock_irq(&ctx->fault_pending_wqh.lock);
     list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
         pending++;
         total++;
     }
     list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
         total++;
     }
     spin_unlock_irq(&ctx->fault_pending_wqh.lock);
 
     /*
      * If more protocols will be added, there will be all shown
      * separated by a space. Like this:
      *  protocols: aa:... bb:...
      */
     seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
            pending, total, UFFD_API, ctx->features,
            UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
 }
 #endif
 
 static const struct file_operations userfaultfd_fops = {
 #ifdef CONFIG_PROC_FS
     .show_fdinfo    = userfaultfd_show_fdinfo,
 #endif
     .release    = userfaultfd_release,
     .poll       = userfaultfd_poll,
     .read       = userfaultfd_read,
     .unlocked_ioctl = userfaultfd_ioctl,
     .compat_ioctl   = compat_ptr_ioctl,
     .llseek     = noop_llseek,
 };
 
 static void init_once_userfaultfd_ctx(void *mem)
 {
     struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
 
     init_waitqueue_head(&ctx->fault_pending_wqh);
     init_waitqueue_head(&ctx->fault_wqh);
     init_waitqueue_head(&ctx->event_wqh);
     init_waitqueue_head(&ctx->fd_wqh);
     seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
 }
 
 SYSCALL_DEFINE1(userfaultfd, int, flags)
 {
     struct userfaultfd_ctx *ctx;
     int fd;
 
     if (!sysctl_unprivileged_userfaultfd &&
         (flags & UFFD_USER_MODE_ONLY) == 0 &&
         !capable(CAP_SYS_PTRACE)) {
         printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
             "sysctl knob to 1 if kernel faults must be handled "
             "without obtaining CAP_SYS_PTRACE capability\n");
         return -EPERM;
     }
 
     BUG_ON(!current->mm);
 
     /* Check the UFFD_* constants for consistency.  */
     BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
     BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
     BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
 
     if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
         return -EINVAL;
 
     ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
     if (!ctx)
         return -ENOMEM;
 
     refcount_set(&ctx->refcount, 1);
     ctx->flags = flags;
     ctx->features = 0;
     ctx->released = false;
     atomic_set(&ctx->mmap_changing, 0);
     ctx->mm = current->mm;
     /* prevent the mm struct to be freed */
     mmgrab(ctx->mm);
 
     fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
             O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
     if (fd < 0) {
         mmdrop(ctx->mm);
         kmem_cache_free(userfaultfd_ctx_cachep, ctx);
     }
     return fd;
 }
 
 static int __init userfaultfd_init(void)
 {
     userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
                         sizeof(struct userfaultfd_ctx),
                         0,
                         SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                         init_once_userfaultfd_ctx);
     return 0;
 }
 __initcall(userfaultfd_init);

This page was automatically generated by the 2.1.0 LXR engine. The LXR team