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

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Date:   Tue, 14 Jul 2020 12:17:50 -0700
From:   Matthew Garrett <mjg59@...gle.com>
To:     Chris Down <chris@...isdown.name>
Cc:     Borislav Petkov <bp@...en8.de>,
        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, Jul 14, 2020 at 9:04 AM Chris Down <chris@...isdown.name> wrote:
> Either way, again, this isn't really the point. :-) The point is that there
> _are_ currently widespread cases involving poking MSRs from userspace, however
> sacrilegious or ugly (which I agree with!), and while people should be told
> about that, it's excessive to have the potential to take up 80% of kmsg in the
> default configuration. It doesn't take thousands of messages to get the message
> across, that's what a custom printk ratelimit is for.

Agreed - we should now offer all the necessary interfaces to avoid
userspace having to hit MSRs directly for thermal management, but that
wasn't always the case, and as a result there's tooling that still
behaves this way.