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

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Message-ID: <CAJvTdKmSxkCtBRkL+qP7aaw19amHKBKzNG+z+SuSNo54RBKbyQ@mail.gmail.com>
Date:   Tue, 31 Aug 2021 18:44:28 -0400
From:   Len Brown <lenb@...nel.org>
To:     Thiago Macieira <thiago.macieira@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        "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>,
        "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 Tue, Aug 31, 2021 at 6:39 PM Thiago Macieira
<thiago.macieira@...el.com> wrote:
>
> On Tuesday, 31 August 2021 15:15:55 PDT Len Brown wrote:
> > Indeed, I believe that there is universal agreement that a synchronous
> > return code
> > from a system call is a far superior programming model than decoding
> > the location of a failure in a system call.  (no, the IP isn't random -- it
> > is always the 1st instruction in that thread to touch a TMM register).
>
> That instruction is actually likely going to be a memory load, probably an
> LDTILECFG.

There is no fault on LDTILECONFIG, it will occur on the load tile data.
But yes, still a memory load (with a TMM destination)

Len Brown, Intel Open Source Technology Center