Re: [RFC PATCH v4 03/27] x86/fpu/xstate: Enable XSAVES system states

Yu-cheng Yu
2018-10-04T15:54:02Z

On Tue, 2018-10-02 at 19:15 +0200, Borislav Petkov wrote:
> On Fri, Sep 21, 2018 at 08:03:27AM -0700, Yu-cheng Yu wrote:
> >
> > diff --git a/arch/x86/include/asm/fpu/xstate.h
> > b/arch/x86/include/asm/fpu/xstate.h
> > index 9b382e5157ed..a32dc5f8c963 100644
> > --- a/arch/x86/include/asm/fpu/xstate.h
> > +++ b/arch/x86/include/asm/fpu/xstate.h
> > @@ -19,10 +19,10 @@
> > #define XSAVE_YMM_SIZE 256
> > #define XSAVE_YMM_OFFSET (XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET)
> >
> > -/* System features */
> > -#define XFEATURE_MASK_SYSTEM (XFEATURE_MASK_PT)
>
> Previous patch renames it, this patch deletes it. Why do we need all
> that unnecessary churn?
>
> Also, this patch is trying to do a couple of things at once and
> reviewing it is not trivial. Please split the changes logically.

Yes, if we leave XFEATURE_MASK_SUPERVISOR unchanged in the previous patch, this
patch becomes much simpler. Perhaps we don't even need to split this one.

> > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> > index 19f8df54c72a..dd2c561c4544 100644
> > --- a/arch/x86/kernel/fpu/xstate.c
> > +++ b/arch/x86/kernel/fpu/xstate.c
> > @@ -51,13 +51,16 @@ static short xsave_cpuid_features[] __initdata = {
> > };
> >
> > /*
> > - * Mask of xstate features supported by the CPU and the kernel:
> > + * Mask of xstate features supported by the CPU and the kernel.
> > + * This is the result from CPUID query, SUPPORTED_XFEATURES_MASK,
> > + * and boot_cpu_has().
> > */
>
> This needs to explain what both masks are - user and system. "CPU" and
> "kernel" is not "user" and "all".
>
> > u64 xfeatures_mask_user __read_mostly;
> > +u64 xfeatures_mask_all __read_mostly;

The first one is all supported "user" states; the latter is "system" and "user"
states combined. I will put in comments.

Yu-cheng