linux-kernel - Re: [PATCH -v2.1] x86/msr: Filter MSR writes

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Date:   Wed, 18 Nov 2020 09:58:49 +0100
From:   Mathieu Chouquet-Stringer <me@...hieu.digital>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Matthew Garrett <mjg59@...gle.com>,
        Chris Down <chris@...isdown.name>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        sean.j.christopherson@...el.com, tony.luck@...el.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        the arch/x86 maintainers <x86@...nel.org>, kernel-team@...com
Subject: Re: [PATCH -v2.1] x86/msr: Filter MSR writes

On Tue, Nov 17, 2020 at 10:20:16PM +0100, Borislav Petkov wrote:
> Not for long:
> 
> https://git.kernel.org/tip/fe0a5788624c8b8f113a35bbe4636e37f9321241

That's fantastic.

> Because if you poke at random MSRs and you manage to "configure" your
> CPU to run "out of spec" - this is what the taint flag is called:
> TAINT_CPU_OUT_OF_SPEC - then this is exactly the case you've created: a
> CPU executing outside of specifications.

Don't get me wrong, it makes total sense to do that, it's just the
original reason of !SMP-capable isn't so clear while CPU out of spec is.

-- 
Mathieu Chouquet-Stringer                             me@...hieu.digital
            The sun itself sees not till heaven clears.
	             -- William Shakespeare --