linux-kernel - Re: [PATCH v8 03/27] x86/fpu/xstate: Change names to separate XSAVES system and user states

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Date:   Wed, 21 Aug 2019 16:45:37 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
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>,
        Eugene Syromiatnikov <esyr@...hat.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>,
        Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH v8 03/27] x86/fpu/xstate: Change names to separate XSAVES
 system and user states

On Tue, Aug 13, 2019 at 01:52:01PM -0700, Yu-cheng Yu wrote:
> Control-flow Enforcement (CET) MSR contents are XSAVES system states.
> To support CET, introduce XSAVES system states first.
> 
> XSAVES is a "supervisor" instruction and, comparing to XSAVE, saves
> additional "supervisor" states that can be modified only from CPL 0.
> However, these states are per-task and not kernel's own.  Rename
> "supervisor" states to "system" states to clearly separate them from
> "user" states.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> ---
>  arch/x86/include/asm/fpu/internal.h |  4 +-
>  arch/x86/include/asm/fpu/xstate.h   | 20 +++----
>  arch/x86/kernel/fpu/init.c          |  2 +-
>  arch/x86/kernel/fpu/signal.c        | 10 ++--
>  arch/x86/kernel/fpu/xstate.c        | 86 ++++++++++++++---------------
>  5 files changed, 60 insertions(+), 62 deletions(-)

...

> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index e5cb67d67c03..d560e8861a3c 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -54,13 +54,16 @@ static short xsave_cpuid_features[] __initdata = {
>  };
>  
>  /*
> - * Mask of xstate features supported by the CPU and the kernel:
> + * XSAVES system states can only be modified from CPL 0 and saved by
> + * XSAVES.  The rest are user states.  The following is a mask of
> + * supported user state features derived from boot_cpu_has() and

...derived from detected CPUID feature flags and
SUPPORTED_XFEATURES_MASK.

-- 
Regards/Gruss,
    Boris.

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