Re: [PATCH 17/22] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD

Borislav Petkov
2019-01-30T11:56:14Z

On Wed, Jan 09, 2019 at 12:47:39PM +0100, Sebastian Andrzej Siewior wrote:
> From: Rik van Riel <riel@surriel.com>
>
> The FPU registers need only to be saved if TIF_NEED_FPU_LOAD is not set.
> Otherwise this has been already done and can be skipped.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> arch/x86/kernel/fpu/signal.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> index bf4e6caad305e..a25be217f9a2c 100644
> --- a/arch/x86/kernel/fpu/signal.c
> +++ b/arch/x86/kernel/fpu/signal.c
> @@ -156,7 +156,16 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
> sizeof(struct user_i387_ia32_struct), NULL,
> (struct _fpstate_32 __user *) buf) ? -1 : 1;
>
> - copy_fpregs_to_fpstate(fpu);
> + __fpregs_changes_begin();
> + /*
> + * If we do not need to load the FPU registers at return to userspace
> + * then the CPU has the current state and we need to save it. Otherwise
> + * it is already done and we can skip it.
> + */
> + if (!test_thread_flag(TIF_NEED_FPU_LOAD))
> + copy_fpregs_to_fpstate(fpu);

I wonder if this flag would make the code more easy to follow by calling
it

TIF_FPU_REGS_VALID

instead, to denote that the FPU registers in the CPU have a valid
content.

Then the test becomes:

if (test_thread_flag(TIF_FPU_REGS_VALID))
copy_fpregs_to_fpstate(fpu);

--
Regards/Gruss,
Boris.

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