cb3ea4b767
We don't set it on PF_KTHREAD threads as they never return to userspace, and PF_IO_WORKER threads are identical in that regard. As they keep running in the kernel until they die, skip setting the FPU flag on them. More of a cosmetic thing that was found while debugging and issue and pondering why the FPU flag is set on these threads. Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Link: https://lore.kernel.org/r/560c844c-f128-555b-40c6-31baff27537f@kernel.dk
68 lines
2 KiB
C
68 lines
2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_FPU_SCHED_H
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#define _ASM_X86_FPU_SCHED_H
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#include <linux/sched.h>
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#include <asm/cpufeature.h>
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#include <asm/fpu/types.h>
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#include <asm/trace/fpu.h>
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extern void save_fpregs_to_fpstate(struct fpu *fpu);
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extern void fpu__drop(struct fpu *fpu);
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extern int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal);
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extern void fpu_flush_thread(void);
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/*
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* FPU state switching for scheduling.
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*
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* This is a two-stage process:
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*
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* - switch_fpu_prepare() saves the old state.
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* This is done within the context of the old process.
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*
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* - switch_fpu_finish() sets TIF_NEED_FPU_LOAD; the floating point state
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* will get loaded on return to userspace, or when the kernel needs it.
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*
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* If TIF_NEED_FPU_LOAD is cleared then the CPU's FPU registers
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* are saved in the current thread's FPU register state.
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*
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* If TIF_NEED_FPU_LOAD is set then CPU's FPU registers may not
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* hold current()'s FPU registers. It is required to load the
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* registers before returning to userland or using the content
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* otherwise.
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*
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* The FPU context is only stored/restored for a user task and
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* PF_KTHREAD is used to distinguish between kernel and user threads.
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*/
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static inline void switch_fpu_prepare(struct fpu *old_fpu, int cpu)
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{
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if (cpu_feature_enabled(X86_FEATURE_FPU) &&
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!(current->flags & (PF_KTHREAD | PF_IO_WORKER))) {
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save_fpregs_to_fpstate(old_fpu);
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/*
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* The save operation preserved register state, so the
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* fpu_fpregs_owner_ctx is still @old_fpu. Store the
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* current CPU number in @old_fpu, so the next return
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* to user space can avoid the FPU register restore
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* when is returns on the same CPU and still owns the
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* context.
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*/
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old_fpu->last_cpu = cpu;
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trace_x86_fpu_regs_deactivated(old_fpu);
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}
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}
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/*
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* Delay loading of the complete FPU state until the return to userland.
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* PKRU is handled separately.
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*/
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static inline void switch_fpu_finish(void)
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{
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if (cpu_feature_enabled(X86_FEATURE_FPU))
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set_thread_flag(TIF_NEED_FPU_LOAD);
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}
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#endif /* _ASM_X86_FPU_SCHED_H */
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