linux-kernel - Re: [PATCH] x86/cpu: Avoid writing MSR_IA32_TSX

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Date:   Tue, 6 Sep 2022 22:43:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH] x86/cpu: Avoid writing MSR_IA32_TSX_CTRL when writing it
 is not supported

On Tue, Sep 06, 2022 at 10:17:43PM +0200, Hans de Goede wrote:
> On an Intel Atom N2600 (and presumable other Cedar Trail models)
> MSR_IA32_TSX_CTRL can be read, causing saved_msr.valid to be set for it
> by msr_build_context().
> 
> This causes restore_processor_state() to try and restore it, but writing
> this MSR is not allowed on the Intel Atom N2600 leading to:

FWIW, virt tends to do this same thing a lot. They'll allow reading
random MSRs and only fail on write.