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SubjectRe: [PATCH 10/11] x86/fpu: prepare copy_fpstate_to_sigframe for TIF_LOAD_FPU
On 2018-10-12 12:40:19 [-0700], Dave Hansen wrote:
> On 10/04/2018 07:05 AM, Sebastian Andrzej Siewior wrote:
> > From: Rik van Riel <riel@surriel.com>
> >
> > If TIF_LOAD_FPU is set, then the registers are saved (not loaded). In that case
> > we skip the saving part.
>
> This sentence hurts my brain.
>
> "If TIF_LOAD_FPU is set the registers are ... not loaded"
>
> I think that means that something could use some better naming.
>
> Should TIF_LOAD_FPU be TIF_NEED_FPU_LOAD, perhaps?

ARM has TIF_FOREIGN_FPSTATE which basically means that the current FP
stat does not belong to current().
Let me try to use TIF_NEED_FPU_LOAD and see how that works out.

> > Signed-off-by: Rik van Riel <riel@surriel.com>
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> > arch/x86/kernel/fpu/signal.c | 16 ++++++++++------
> > 1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> > index c8f5ff58578ed..979dcd1ed82e0 100644
> > --- a/arch/x86/kernel/fpu/signal.c
> > +++ b/arch/x86/kernel/fpu/signal.c
> > @@ -155,13 +155,17 @@ 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;
> >
> > - /* Update the thread's fxstate to save the fsave header. */
> > - if (ia32_fxstate) {
> > - copy_fxregs_to_kernel(fpu);
> > - } else {
> > - copy_fpregs_to_fpstate(fpu);
> > - fpregs_deactivate(fpu);
> > + __fpregs_changes_begin();
> > + if (!test_thread_flag(TIF_LOAD_FPU)) {
>
> This needs commenting, please.
>
> If we do not need to load the FPU at return to userspace, it means the
> state is in the the registers, not the buffer. So, update the buffer to
> match the registers.

okay. Let me add this then.

Sebastian

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