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

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Date:   Thu, 04 Oct 2018 08:47:35 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v4 03/27] x86/fpu/xstate: Enable XSAVES system states

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