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 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (c) 2017-2019 Borislav Petkov, SUSE Labs.
  */
 #include <linux/mm.h>
 #include <linux/gfp.h>
 #include <linux/ras.h>
 #include <linux/kernel.h>
 #include <linux/workqueue.h>
 
 #include <asm/mce.h>
 
 #include "debugfs.h"
 
 /*
  * RAS Correctable Errors Collector
  *
  * This is a simple gadget which collects correctable errors and counts their
  * occurrence per physical page address.
  *
  * We've opted for possibly the simplest data structure to collect those - an
  * array of the size of a memory page. It stores 512 u64's with the following
  * structure:
  *
  * [63 ... PFN ... 12 | 11 ... generation ... 10 | 9 ... count ... 0]
  *
  * The generation in the two highest order bits is two bits which are set to 11b
  * on every insertion. During the course of each entry's existence, the
  * generation field gets decremented during spring cleaning to 10b, then 01b and
  * then 00b.
  *
  * This way we're employing the natural numeric ordering to make sure that newly
  * inserted/touched elements have higher 12-bit counts (which we've manufactured)
  * and thus iterating over the array initially won't kick out those elements
  * which were inserted last.
  *
  * Spring cleaning is what we do when we reach a certain number CLEAN_ELEMS of
  * elements entered into the array, during which, we're decaying all elements.
  * If, after decay, an element gets inserted again, its generation is set to 11b
  * to make sure it has higher numerical count than other, older elements and
  * thus emulate an LRU-like behavior when deleting elements to free up space
  * in the page.
  *
  * When an element reaches it's max count of action_threshold, we try to poison
  * it by assuming that errors triggered action_threshold times in a single page
  * are excessive and that page shouldn't be used anymore. action_threshold is
  * initialized to COUNT_MASK which is the maximum.
  *
  * That error event entry causes cec_add_elem() to return !0 value and thus
  * signal to its callers to log the error.
  *
  * To the question why we've chosen a page and moving elements around with
  * memmove(), it is because it is a very simple structure to handle and max data
  * movement is 4K which on highly optimized modern CPUs is almost unnoticeable.
  * We wanted to avoid the pointer traversal of more complex structures like a
  * linked list or some sort of a balancing search tree.
  *
  * Deleting an element takes O(n) but since it is only a single page, it should
  * be fast enough and it shouldn't happen all too often depending on error
  * patterns.
  */
 
 #undef pr_fmt
 #define pr_fmt(fmt) "RAS: " fmt
 
 /*
  * We use DECAY_BITS bits of PAGE_SHIFT bits for counting decay, i.e., how long
  * elements have stayed in the array without having been accessed again.
  */
 #define DECAY_BITS      2
 #define DECAY_MASK      ((1ULL << DECAY_BITS) - 1)
 #define MAX_ELEMS       (PAGE_SIZE / sizeof(u64))
 
 /*
  * Threshold amount of inserted elements after which we start spring
  * cleaning.
  */
 #define CLEAN_ELEMS     (MAX_ELEMS >> DECAY_BITS)
 
 /* Bits which count the number of errors happened in this 4K page. */
 #define COUNT_BITS      (PAGE_SHIFT - DECAY_BITS)
 #define COUNT_MASK      ((1ULL << COUNT_BITS) - 1)
 #define FULL_COUNT_MASK     (PAGE_SIZE - 1)
 
 /*
  * u64: [ 63 ... 12 | DECAY_BITS | COUNT_BITS ]
  */
 
 #define PFN(e)          ((e) >> PAGE_SHIFT)
 #define DECAY(e)        (((e) >> COUNT_BITS) & DECAY_MASK)
 #define COUNT(e)        ((unsigned int)(e) & COUNT_MASK)
 #define FULL_COUNT(e)       ((e) & (PAGE_SIZE - 1))
 
 static struct ce_array {
     u64 *array;         /* container page */
     unsigned int n;         /* number of elements in the array */
 
     unsigned int decay_count;   /*
                      * number of element insertions/increments
                      * since the last spring cleaning.
                      */
 
     u64 pfns_poisoned;      /*
                      * number of PFNs which got poisoned.
                      */
 
     u64 ces_entered;        /*
                      * The number of correctable errors
                      * entered into the collector.
                      */
 
     u64 decays_done;        /*
                      * Times we did spring cleaning.
                      */
 
     union {
         struct {
             __u32   disabled : 1,   /* cmdline disabled */
             __resv   : 31;
         };
         __u32 flags;
     };
 } ce_arr;
 
 static DEFINE_MUTEX(ce_mutex);
 static u64 dfs_pfn;
 
 /* Amount of errors after which we offline */
 static u64 action_threshold = COUNT_MASK;
 
 /* Each element "decays" each decay_interval which is 24hrs by default. */
 #define CEC_DECAY_DEFAULT_INTERVAL  24 * 60 * 60    /* 24 hrs */
 #define CEC_DECAY_MIN_INTERVAL       1 * 60 * 60    /* 1h */
 #define CEC_DECAY_MAX_INTERVAL     30 * 24 * 60 * 60    /* one month */
 static struct delayed_work cec_work;
 static u64 decay_interval = CEC_DECAY_DEFAULT_INTERVAL;
 
 /*
  * Decrement decay value. We're using DECAY_BITS bits to denote decay of an
  * element in the array. On insertion and any access, it gets reset to max.
  */
 static void do_spring_cleaning(struct ce_array *ca)
 {
     int i;
 
     for (i = 0; i < ca->n; i++) {
         u8 decay = DECAY(ca->array[i]);
 
         if (!decay)
             continue;
 
         decay--;
 
         ca->array[i] &= ~(DECAY_MASK << COUNT_BITS);
         ca->array[i] |= (decay << COUNT_BITS);
     }
     ca->decay_count = 0;
     ca->decays_done++;
 }
 
 /*
  * @interval in seconds
  */
 static void cec_mod_work(unsigned long interval)
 {
     unsigned long iv;
 
     iv = interval * HZ;
     mod_delayed_work(system_wq, &cec_work, round_jiffies(iv));
 }
 
 static void cec_work_fn(struct work_struct *work)
 {
     mutex_lock(&ce_mutex);
     do_spring_cleaning(&ce_arr);
     mutex_unlock(&ce_mutex);
 
     cec_mod_work(decay_interval);
 }
 
 /*
  * @to: index of the smallest element which is >= then @pfn.
  *
  * Return the index of the pfn if found, otherwise negative value.
  */
 static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
 {
     int min = 0, max = ca->n - 1;
     u64 this_pfn;
 
     while (min <= max) {
         int i = (min + max) >> 1;
 
         this_pfn = PFN(ca->array[i]);
 
         if (this_pfn < pfn)
             min = i + 1;
         else if (this_pfn > pfn)
             max = i - 1;
         else if (this_pfn == pfn) {
             if (to)
                 *to = i;
 
             return i;
         }
     }
 
     /*
      * When the loop terminates without finding @pfn, min has the index of
      * the element slot where the new @pfn should be inserted. The loop
      * terminates when min > max, which means the min index points to the
      * bigger element while the max index to the smaller element, in-between
      * which the new @pfn belongs to.
      *
      * For more details, see exercise 1, Section 6.2.1 in TAOCP, vol. 3.
      */
     if (to)
         *to = min;
 
     return -ENOKEY;
 }
 
 static int find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
 {
     WARN_ON(!to);
 
     if (!ca->n) {
         *to = 0;
         return -ENOKEY;
     }
     return __find_elem(ca, pfn, to);
 }
 
 static void del_elem(struct ce_array *ca, int idx)
 {
     /* Save us a function call when deleting the last element. */
     if (ca->n - (idx + 1))
         memmove((void *)&ca->array[idx],
             (void *)&ca->array[idx + 1],
             (ca->n - (idx + 1)) * sizeof(u64));
 
     ca->n--;
 }
 
 static u64 del_lru_elem_unlocked(struct ce_array *ca)
 {
     unsigned int min = FULL_COUNT_MASK;
     int i, min_idx = 0;
 
     for (i = 0; i < ca->n; i++) {
         unsigned int this = FULL_COUNT(ca->array[i]);
 
         if (min > this) {
             min = this;
             min_idx = i;
         }
     }
 
     del_elem(ca, min_idx);
 
     return PFN(ca->array[min_idx]);
 }
 
 /*
  * We return the 0th pfn in the error case under the assumption that it cannot
  * be poisoned and excessive CEs in there are a serious deal anyway.
  */
 static u64 __maybe_unused del_lru_elem(void)
 {
     struct ce_array *ca = &ce_arr;
     u64 pfn;
 
     if (!ca->n)
         return 0;
 
     mutex_lock(&ce_mutex);
     pfn = del_lru_elem_unlocked(ca);
     mutex_unlock(&ce_mutex);
 
     return pfn;
 }
 
 static bool sanity_check(struct ce_array *ca)
 {
     bool ret = false;
     u64 prev = 0;
     int i;
 
     for (i = 0; i < ca->n; i++) {
         u64 this = PFN(ca->array[i]);
 
         if (WARN(prev > this, "prev: 0x%016llx <-> this: 0x%016llx\n", prev, this))
             ret = true;
 
         prev = this;
     }
 
     if (!ret)
         return ret;
 
     pr_info("Sanity check dump:\n{ n: %d\n", ca->n);
     for (i = 0; i < ca->n; i++) {
         u64 this = PFN(ca->array[i]);
 
         pr_info(" %03d: [%016llx|%03llx]\n", i, this, FULL_COUNT(ca->array[i]));
     }
     pr_info("}\n");
 
     return ret;
 }
 
 /**
  * cec_add_elem - Add an element to the CEC array.
  * @pfn:    page frame number to insert
  *
  * Return values:
  * - <0:    on error
  * -  0:    on success
  * - >0:    when the inserted pfn was offlined
  */
 static int cec_add_elem(u64 pfn)
 {
     struct ce_array *ca = &ce_arr;
     int count, err, ret = 0;
     unsigned int to = 0;
 
     /*
      * We can be called very early on the identify_cpu() path where we are
      * not initialized yet. We ignore the error for simplicity.
      */
     if (!ce_arr.array || ce_arr.disabled)
         return -ENODEV;
 
     mutex_lock(&ce_mutex);
 
     ca->ces_entered++;
 
     /* Array full, free the LRU slot. */
     if (ca->n == MAX_ELEMS)
         WARN_ON(!del_lru_elem_unlocked(ca));
 
     err = find_elem(ca, pfn, &to);
     if (err < 0) {
         /*
          * Shift range [to-end] to make room for one more element.
          */
         memmove((void *)&ca->array[to + 1],
             (void *)&ca->array[to],
             (ca->n - to) * sizeof(u64));
 
         ca->array[to] = pfn << PAGE_SHIFT;
         ca->n++;
     }
 
     /* Add/refresh element generation and increment count */
     ca->array[to] |= DECAY_MASK << COUNT_BITS;
     ca->array[to]++;
 
     /* Check action threshold and soft-offline, if reached. */
     count = COUNT(ca->array[to]);
     if (count >= action_threshold) {
         u64 pfn = ca->array[to] >> PAGE_SHIFT;
 
         if (!pfn_valid(pfn)) {
             pr_warn("CEC: Invalid pfn: 0x%llx\n", pfn);
         } else {
             /* We have reached max count for this page, soft-offline it. */
             pr_err("Soft-offlining pfn: 0x%llx\n", pfn);
             memory_failure_queue(pfn, MF_SOFT_OFFLINE);
             ca->pfns_poisoned++;
         }
 
         del_elem(ca, to);
 
         /*
          * Return a >0 value to callers, to denote that we've reached
          * the offlining threshold.
          */
         ret = 1;
 
         goto unlock;
     }
 
     ca->decay_count++;
 
     if (ca->decay_count >= CLEAN_ELEMS)
         do_spring_cleaning(ca);
 
     WARN_ON_ONCE(sanity_check(ca));
 
 unlock:
     mutex_unlock(&ce_mutex);
 
     return ret;
 }
 
 static int u64_get(void *data, u64 *val)
 {
     *val = *(u64 *)data;
 
     return 0;
 }
 
 static int pfn_set(void *data, u64 val)
 {
     *(u64 *)data = val;
 
     cec_add_elem(val);
 
     return 0;
 }
 
 DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");
 
 static int decay_interval_set(void *data, u64 val)
 {
     if (val < CEC_DECAY_MIN_INTERVAL)
         return -EINVAL;
 
     if (val > CEC_DECAY_MAX_INTERVAL)
         return -EINVAL;
 
     *(u64 *)data   = val;
     decay_interval = val;
 
     cec_mod_work(decay_interval);
 
     return 0;
 }
 DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n");
 
 static int action_threshold_set(void *data, u64 val)
 {
     *(u64 *)data = val;
 
     if (val > COUNT_MASK)
         val = COUNT_MASK;
 
     action_threshold = val;
 
     return 0;
 }
 DEFINE_DEBUGFS_ATTRIBUTE(action_threshold_ops, u64_get, action_threshold_set, "%lld\n");
 
 static const char * const bins[] = { "00", "01", "10", "11" };
 
 static int array_show(struct seq_file *m, void *v)
 {
     struct ce_array *ca = &ce_arr;
     int i;
 
     mutex_lock(&ce_mutex);
 
     seq_printf(m, "{ n: %d\n", ca->n);
     for (i = 0; i < ca->n; i++) {
         u64 this = PFN(ca->array[i]);
 
         seq_printf(m, " %3d: [%016llx|%s|%03llx]\n",
                i, this, bins[DECAY(ca->array[i])], COUNT(ca->array[i]));
     }
 
     seq_printf(m, "}\n");
 
     seq_printf(m, "Stats:\nCEs: %llu\nofflined pages: %llu\n",
            ca->ces_entered, ca->pfns_poisoned);
 
     seq_printf(m, "Flags: 0x%x\n", ca->flags);
 
     seq_printf(m, "Decay interval: %lld seconds\n", decay_interval);
     seq_printf(m, "Decays: %lld\n", ca->decays_done);
 
     seq_printf(m, "Action threshold: %lld\n", action_threshold);
 
     mutex_unlock(&ce_mutex);
 
     return 0;
 }
 
 DEFINE_SHOW_ATTRIBUTE(array);
 
 static int __init create_debugfs_nodes(void)
 {
     struct dentry *d, *pfn, *decay, *count, *array;
 
     d = debugfs_create_dir("cec", ras_debugfs_dir);
     if (!d) {
         pr_warn("Error creating cec debugfs node!\n");
         return -1;
     }
 
     decay = debugfs_create_file("decay_interval", S_IRUSR | S_IWUSR, d,
                     &decay_interval, &decay_interval_ops);
     if (!decay) {
         pr_warn("Error creating decay_interval debugfs node!\n");
         goto err;
     }
 
     count = debugfs_create_file("action_threshold", S_IRUSR | S_IWUSR, d,
                     &action_threshold, &action_threshold_ops);
     if (!count) {
         pr_warn("Error creating action_threshold debugfs node!\n");
         goto err;
     }
 
     if (!IS_ENABLED(CONFIG_RAS_CEC_DEBUG))
         return 0;
 
     pfn = debugfs_create_file("pfn", S_IRUSR | S_IWUSR, d, &dfs_pfn, &pfn_ops);
     if (!pfn) {
         pr_warn("Error creating pfn debugfs node!\n");
         goto err;
     }
 
     array = debugfs_create_file("array", S_IRUSR, d, NULL, &array_fops);
     if (!array) {
         pr_warn("Error creating array debugfs node!\n");
         goto err;
     }
 
     return 0;
 
 err:
     debugfs_remove_recursive(d);
 
     return 1;
 }
 
 static int cec_notifier(struct notifier_block *nb, unsigned long val,
             void *data)
 {
     struct mce *m = (struct mce *)data;
 
     if (!m)
         return NOTIFY_DONE;
 
     /* We eat only correctable DRAM errors with usable addresses. */
     if (mce_is_memory_error(m) &&
         mce_is_correctable(m)  &&
         mce_usable_address(m)) {
         if (!cec_add_elem(m->addr >> PAGE_SHIFT)) {
             m->kflags |= MCE_HANDLED_CEC;
             return NOTIFY_OK;
         }
     }
 
     return NOTIFY_DONE;
 }
 
 static struct notifier_block cec_nb = {
     .notifier_call  = cec_notifier,
     .priority   = MCE_PRIO_CEC,
 };
 
 static int __init cec_init(void)
 {
     if (ce_arr.disabled)
         return -ENODEV;
 
     ce_arr.array = (void *)get_zeroed_page(GFP_KERNEL);
     if (!ce_arr.array) {
         pr_err("Error allocating CE array page!\n");
         return -ENOMEM;
     }
 
     if (create_debugfs_nodes()) {
         free_page((unsigned long)ce_arr.array);
         return -ENOMEM;
     }
 
     INIT_DELAYED_WORK(&cec_work, cec_work_fn);
     schedule_delayed_work(&cec_work, CEC_DECAY_DEFAULT_INTERVAL);
 
     mce_register_decode_chain(&cec_nb);
 
     pr_info("Correctable Errors collector initialized.\n");
     return 0;
 }
 late_initcall(cec_init);
 
 int __init parse_cec_param(char *str)
 {
     if (!str)
         return 0;
 
     if (*str == '=')
         str++;
 
     if (!strcmp(str, "cec_disable"))
         ce_arr.disabled = 1;
     else
         return 0;
 
     return 1;
 }

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