linux-kernel - Re: [PATCH] x86: also disable FSRM if ERMS is disabled

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Message-ID: <Y0XYhftUTqd2BDHn@zn.tnic>
Date:   Tue, 11 Oct 2022 22:56:37 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Daniel Verkamp <dverkamp@...omium.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>
Subject: Re: [PATCH] x86: also disable FSRM if ERMS is disabled

On Tue, Oct 11, 2022 at 07:08:51PM +0000, Luck, Tony wrote:
> I don't think Intel will deliberately release a CPU that has FSRM=1, ERMS=0.

Sure, but I don't mean that. Rather: if for some reason the kernel or
BIOS is supposed to fix an erratum related to those enhanced REP moving
routines and goes and clears the MSR bit.

That won't help because userspace will still use them since the CPUID
flags remain set.

I guess such a case is probably not going to happen in real life but if
it happened, that bit clearing is kinda useless.

I'd say.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette