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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH] x86/msr: Block writes to certain MSRs unconditionally
Date:   Sun, 11 Apr 2021 09:57:20 -0700
Message-Id: <C7F7BE8D-562B-4BC3-A209-8EDD7DAF0AAA@amacapital.net>
References: <20210411164342.GL3762101@tassilo.jf.intel.com>
Cc:     Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Feng Tang <feng.tang@intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Zhang, Rui" <rui.zhang@intel.com>,
        "Kleen, Andi" <andi.kleen@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Len Brown <len.brown@intel.com>
In-Reply-To: <20210411164342.GL3762101@tassilo.jf.intel.com>
To:     Andi Kleen <ak@linux.intel.com>
Precedence: bulk


> On Apr 11, 2021, at 9:43 AM, Andi Kleen <ak@linux.intel.com> wrote:
>=20
> =EF=BB=BF
>>=20
>> I have actually seen real user programs poke MSR_SYSCALL_MASK.
>=20
> Hmm, what was the use case?
>=20
>=20

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