linux-kernel - Re: [PATCH] x86/msr: Block writes to certain MSRs unconditionally

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Message-Id: <C7F7BE8D-562B-4BC3-A209-8EDD7DAF0AAA@amacapital.net>
Date:   Sun, 11 Apr 2021 09:57:20 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Feng Tang <feng.tang@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Len Brown <len.brown@...el.com>
Subject: Re: [PATCH] x86/msr: Block writes to certain MSRs unconditionally




> On Apr 11, 2021, at 9:43 AM, Andi Kleen <ak@...ux.intel.com> wrote:
> 
> 
>> 
>> I have actually seen real user programs poke MSR_SYSCALL_MASK.
> 
> Hmm, what was the use case?
> 
> 

Working around a kernel bug.  The workaround only worked on AMD systems.  The correct solution was to fix the kernel bug, not poke MSRs.