asm/fpu/sched.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 #ifndef _ASM_X86_FPU_SCHED_H
0003 #define _ASM_X86_FPU_SCHED_H
0004
0005 #include <linux/sched.h>
0006
0007 #include <asm/cpufeature.h>
0008 #include <asm/fpu/types.h>
0009
0010 #include <asm/trace/fpu.h>
0011
0012 extern void save_fpregs_to_fpstate(struct fpu *fpu);
0013 extern void fpu__drop(struct fpu *fpu);
0014 extern int  fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal);
0015 extern void fpu_flush_thread(void);
0016
0017 /*
0018  * FPU state switching for scheduling.
0019  *
0020  * This is a two-stage process:
0021  *
0022  *  - switch_fpu_prepare() saves the old state.
0023  *    This is done within the context of the old process.
0024  *
0025  *  - switch_fpu_finish() sets TIF_NEED_FPU_LOAD; the floating point state
0026  *    will get loaded on return to userspace, or when the kernel needs it.
0027  *
0028  * If TIF_NEED_FPU_LOAD is cleared then the CPU's FPU registers
0029  * are saved in the current thread's FPU register state.
0030  *
0031  * If TIF_NEED_FPU_LOAD is set then CPU's FPU registers may not
0032  * hold current()'s FPU registers. It is required to load the
0033  * registers before returning to userland or using the content
0034  * otherwise.
0035  *
0036  * The FPU context is only stored/restored for a user task and
0037  * PF_KTHREAD is used to distinguish between kernel and user threads.
0038  */
0039 static inline void switch_fpu_prepare(struct fpu *old_fpu, int cpu)
0040 {
0041     if (cpu_feature_enabled(X86_FEATURE_FPU) &&
0042         !(current->flags & PF_KTHREAD)) {
0043         save_fpregs_to_fpstate(old_fpu);
0044         /*
0045          * The save operation preserved register state, so the
0046          * fpu_fpregs_owner_ctx is still @old_fpu. Store the
0047          * current CPU number in @old_fpu, so the next return
0048          * to user space can avoid the FPU register restore
0049          * when is returns on the same CPU and still owns the
0050          * context.
0051          */
0052         old_fpu->last_cpu = cpu;
0053
0054         trace_x86_fpu_regs_deactivated(old_fpu);
0055     }
0056 }
0057
0058 /*
0059  * Delay loading of the complete FPU state until the return to userland.
0060  * PKRU is handled separately.
0061  */
0062 static inline void switch_fpu_finish(void)
0063 {
0064     if (cpu_feature_enabled(X86_FEATURE_FPU))
0065         set_thread_flag(TIF_NEED_FPU_LOAD);
0066 }
0067
0068 #endif /* _ASM_X86_FPU_SCHED_H */