linux-kernel - Re: [PATCH 3/3] x86/msr: Add an MSR write callback

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Message-ID: <20200610123226.GC2497@hirez.programming.kicks-ass.net>
Date:   Wed, 10 Jun 2020 14:32:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     X86 ML <x86@...nel.org>, Tom Lendacky <thomas.lendacky@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Morton <Eric.Morton@....com>
Subject: Re: [PATCH 3/3] x86/msr: Add an MSR write callback

On Wed, Jun 10, 2020 at 01:00:37PM +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> Add a callback which gets executed after a MSR is written from
> userspace. This is needed because in the case of AMD's MSR_AMD64_LS_CFG
> MSR which gets cached in the kernel, the cached value needs to be
> updated after the write, otherwise latter doesn't stick.

We cache a whole bunch of MSRs in kernel. Why is this one special?

If you write using the stupid msr device, you get to keep all pieces.