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Commit eb6a3251 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

x86/fpu: Remove task_disable_lazy_fpu_restore() 



Replace task_disable_lazy_fpu_restore() with easier to read
open-coded uses: we already update the fpu->last_cpu field
explicitly in other cases.

(This also removes yet another task_struct using FPU method.)

Better explain the fpu::last_cpu field in the structure definition.

Reviewed-by: default avatarBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent ca6787ba

arch/x86/include/asm/fpu-internal.h

+2 −12
Original line number Diff line number Diff line
@@ -74,16 +74,6 @@ static inline void __cpu_disable_lazy_restore(unsigned int cpu) 
	per_cpu(fpu_fpregs_owner_ctx, cpu) = NULL;

}



/*

 * Used to indicate that the FPU state in memory is newer than the FPU

 * state in registers, and the FPU state should be reloaded next time the

 * task is run. Only safe on the current task, or non-running tasks.

 */

static inline void task_disable_lazy_fpu_restore(struct task_struct *tsk)

{

	tsk->thread.fpu.last_cpu = ~0;

}



static inline int fpu_lazy_restore(struct task_struct *new, unsigned int cpu)

{

	return &new->thread.fpu == this_cpu_read_stable(fpu_fpregs_owner_ctx) &&
@@ -430,7 +420,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta 


	if (old_fpu->has_fpu) {

		if (!fpu_save_init(&old->thread.fpu))

			task_disable_lazy_fpu_restore(old);

			old->thread.fpu.last_cpu = -1;

		else

			old->thread.fpu.last_cpu = cpu;
@@ -446,7 +436,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta 
			stts();

	} else {

		old->thread.fpu.counter = 0;

		task_disable_lazy_fpu_restore(old);

		old->thread.fpu.last_cpu = -1;

		if (fpu.preload) {

			new->thread.fpu.counter++;

			if (fpu_lazy_restore(new, cpu))

arch/x86/include/asm/fpu/types.h

+11 −0
Original line number Diff line number Diff line
@@ -125,7 +125,18 @@ union thread_xstate { 
};



struct fpu {

	/*

	 * Records the last CPU on which this context was loaded into

	 * FPU registers. (In the lazy-switching case we might be

	 * able to reuse FPU registers across multiple context switches

	 * this way, if no intermediate task used the FPU.)

	 *

	 * A value of -1 is used to indicate that the FPU state in context

	 * memory is newer than the FPU state in registers, and that the

	 * FPU state should be reloaded next time the task is run.

	 */

	unsigned int			last_cpu;



	unsigned int			has_fpu;

	union thread_xstate		*state;

	/*

arch/x86/kernel/fpu/core.c

+2 −3
Original line number Diff line number Diff line
@@ -242,8 +242,7 @@ int fpu__copy(struct task_struct *dst, struct task_struct *src) 
	dst->thread.fpu.counter = 0;

	dst->thread.fpu.has_fpu = 0;

	dst->thread.fpu.state = NULL;



	task_disable_lazy_fpu_restore(dst);

	dst->thread.fpu.last_cpu = -1;



	if (src_fpu->fpstate_active) {

		int err = fpstate_alloc(dst_fpu);
@@ -319,7 +318,7 @@ static int fpu__unlazy_stopped(struct task_struct *child) 
		return -EINVAL;



	if (child_fpu->fpstate_active) {

		task_disable_lazy_fpu_restore(child);

		child->thread.fpu.last_cpu = -1;

		return 0;

	}