linux-kernel - Re: [PATCH v9 12/26] x86/fpu/xstate: Use feature disable (XFD) to protect dynamic user state

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Date:   Tue, 31 Aug 2021 17:44:00 -0400
From:   Len Brown <lenb@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
        "Brown, Len" <len.brown@...el.com>,
        Dave Hansen <dave.hansen@...el.com>, thiago.macieira@...el.com,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 12/26] x86/fpu/xstate: Use feature disable (XFD) to
 protect dynamic user state

On Mon, Aug 30, 2021 at 1:41 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Tue, Aug 24, 2021 at 06:21:23PM -0400, Len Brown wrote:
> > MSR_IA32_XFD and MSR_IA32_XFD_ERR are architectural.
> >
> > (which is why they follow the convention of having an "IA32" in their name)
>
> Where is that official statement I can refer to that says that MSRs with
> "IA32" in the name are architectural?
>
> Perhaps that section of the SDM:
>
> "2.1 ARCHITECTURAL MSRS"

Yes.

> In any case, those MSRs are not there yet, maybe they need to trickle
> from the ISA to the SDM docs at some point first.

Right.
These new MSRs are already named IA32... even though the info from
the ISA Extensions Manual hasn't yet tricked into the SDM, because
they are defined to be architectural from the get-go.

Len Brown, Intel Open Source Technology Center