So fpu__save() does this currently:
copy_fpregs_to_fpstate(fpu);
if (!use_eager_fpu())
fpregs_deactivate(fpu);
... which deactivates the FPU on lazy switching systems unconditionally.
Both usecases of fpu__save() use this function to save the
FPU state into a fpstate: fork()/clone() and math error signal handling.
The unconditional disabling of FPU registers in the lazy switching
case is probably a mistaken conversion of old FNSAVE code (that had
to disable FPU registers).
So speed up this code by only disabling FPU registers when absolutely
necessary: when indicated by the copy_fpregs_to_fpstate() return
code:
if (!copy_fpregs_to_fpstate(fpu))
fpregs_deactivate(fpu);
Reviewed-by: Borislav Petkov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/kernel/fpu/core.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 1e79a6b3fc27..8835b802aa16 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -170,7 +170,7 @@ void irq_ts_restore(int TS_state)
EXPORT_SYMBOL_GPL(irq_ts_restore);
/*
- * Save the FPU state (initialize it if necessary):
+ * Save the FPU state (mark it for reload if necessary):
*
* This only ever gets called for the current task.
*/
@@ -180,8 +180,7 @@ void fpu__save(struct fpu *fpu)
preempt_disable();
if (fpu->fpregs_active) {
- copy_fpregs_to_fpstate(fpu);
- if (!use_eager_fpu())
+ if (!copy_fpregs_to_fpstate(fpu))
fpregs_deactivate(fpu);
}
preempt_enable();
--
2.1.0
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