sched.h

 1/* SPDX-License-Identifier: GPL-2.0 */
 2#ifndef _ASM_X86_FPU_SCHED_H
 3#define _ASM_X86_FPU_SCHED_H
 4
 5#include <linux/sched.h>
 6
 7#include <asm/cpufeature.h>
 8#include <asm/fpu/types.h>
 9
10#include <asm/trace/fpu.h>
11
12extern void save_fpregs_to_fpstate(struct fpu *fpu);
13extern void fpu__drop(struct task_struct *tsk);
14extern int  fpu_clone(struct task_struct *dst, u64 clone_flags, bool minimal,
15		      unsigned long shstk_addr);
16extern void fpu_flush_thread(void);
17
18/*
19 * FPU state switching for scheduling.
20 *
21 * switch_fpu() saves the old state and sets TIF_NEED_FPU_LOAD if
22 * TIF_NEED_FPU_LOAD is not set.  This is done within the context
23 * of the old process.
24 *
25 * Once TIF_NEED_FPU_LOAD is set, it is required to load the
26 * registers before returning to userland or using the content
27 * otherwise.
28 *
29 * The FPU context is only stored/restored for a user task and
30 * PF_KTHREAD is used to distinguish between kernel and user threads.
31 */
32static inline void switch_fpu(struct task_struct *old, int cpu)
33{
34	if (!test_tsk_thread_flag(old, TIF_NEED_FPU_LOAD) &&
35	    cpu_feature_enabled(X86_FEATURE_FPU) &&
36	    !(old->flags & (PF_KTHREAD | PF_USER_WORKER))) {
37		struct fpu *old_fpu = x86_task_fpu(old);
38
39		set_tsk_thread_flag(old, TIF_NEED_FPU_LOAD);
40		save_fpregs_to_fpstate(old_fpu);
41		/*
42		 * The save operation preserved register state, so the
43		 * fpu_fpregs_owner_ctx is still @old_fpu. Store the
44		 * current CPU number in @old_fpu, so the next return
45		 * to user space can avoid the FPU register restore
46		 * when is returns on the same CPU and still owns the
47		 * context. See fpregs_restore_userregs().
48		 */
49		old_fpu->last_cpu = cpu;
50
51		trace_x86_fpu_regs_deactivated(old_fpu);
52	}
53}
54
55#endif /* _ASM_X86_FPU_SCHED_H */