linux-kernel - Re: [PATCH v5 21/28] x86/fpu/amx: Initialize child's AMX state

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Message-ID: <CAJvTdKkTSv7zc2eT1Ni6+k=V_faCCWmMo5oNunQQt-P7FkON-Q@mail.gmail.com>
Date:   Mon, 24 May 2021 14:21:05 -0400
From:   Len Brown <lenb@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "Brown, Len" <len.brown@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 21/28] x86/fpu/amx: Initialize child's AMX state

On Mon, May 24, 2021 at 2:14 PM Andy Lutomirski <luto@...nel.org> wrote:

> What does VOLATILE mean in this context?

Volatile means caller-saved.

Volatile registers can not be used for globals, static, or for
parameter passing.

ie. By the time the callee is running, they must be assumed to be invalid.

This means that any routine, including the target of a system call,
such as fork/clone, can't assume that any data exists in these
registers.

-- 
Len Brown, Intel Open Source Technology Center