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x86/fpu: Simplify and speed up fpu__copy()

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fpu__copy() has a preempt_disable()/enable() pair, which it had to do to
be able to atomically unlazy the current task when doing an FNSAVE.

But we don't unlazy tasks anymore, we always do direct saves/restores of
FPU context.

So remove both the unnecessary critical section, and update the comments.

Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Yu-cheng Yu <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Ingo Molnar 2017-09-23 15:00:14 +02:00
commit e10078eba6
1 changed files with 3 additions and 12 deletions
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15
arch/x86/kernel/fpu/core.c
View file

@ -206,22 +206,13 @@ int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
* Save current FPU registers directly into the child
* FPU context, without any memory-to-memory copying.
*
* We have to do all this with preemption disabled,
* mostly because of the FNSAVE case, because in that
* case we must not allow preemption in the window
* between the FNSAVE and us marking the context lazy.
*
* It shouldn't be an issue as even FNSAVE is plenty
* fast in terms of critical section length.
* ( The function 'fails' in the FNSAVE case, which destroys
* register contents so we have to copy them back. )
*/
preempt_disable();
if (!copy_fpregs_to_fpstate(dst_fpu)) {
memcpy(&src_fpu->state, &dst_fpu->state,
fpu_kernel_xstate_size);
memcpy(&src_fpu->state, &dst_fpu->state, fpu_kernel_xstate_size);
copy_kernel_to_fpregs(&src_fpu->state);
}
preempt_enable();
trace_x86_fpu_copy_src(src_fpu);
trace_x86_fpu_copy_dst(dst_fpu);