linux-kernel - Re: [RESEND PATCH] perf/x86/intel: Fix unchecked MSR access error for Alder Lake N

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Message-ID: <YwOJHLuX57Q4e/wH@worktop.programming.kicks-ass.net>
Date:   Mon, 22 Aug 2022 15:48:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     acme@...hat.com, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com,
        Jianfeng Gao <jianfeng.gao@...el.com>
Subject: Re: [RESEND PATCH] perf/x86/intel: Fix unchecked MSR access error
 for Alder Lake N

On Mon, Aug 22, 2022 at 09:28:31AM -0400, Liang, Kan wrote:
> 
> 
> On 2022-08-19 10:38 a.m., Peter Zijlstra wrote:
> > On Thu, Aug 18, 2022 at 11:15:30AM -0700, kan.liang@...ux.intel.com wrote:
> >> From: Kan Liang <kan.liang@...ux.intel.com>
> >>
> >> For some Alder Lake N machine, the below unchecked MSR access error may be
> >> triggered.
> >>
> >> [ 0.088017] rcu: Hierarchical SRCU implementation.
> >> [ 0.088017] unchecked MSR access error: WRMSR to 0x38f (tried to write
> >> 0x0001000f0000003f) at rIP: 0xffffffffb5684de8 (native_write_msr+0x8/0x30)
> >> [ 0.088017] Call Trace:
> >> [ 0.088017] <TASK>
> >> [ 0.088017] __intel_pmu_enable_all.constprop.46+0x4a/0xa0
> > 
> > FWIW, I seem to get the same error when booting KVM on my ADL. I'm
> > fairly sure the whole CPUID vs vCPU thing is a trainwreck.
> 
> We will enhance the CPUID to address the issues. Hopefully, we can have
> them supported in the next generation.

How!? A vCPU can readily migrate between a big and small CPU. There is
no way the guest can sanely program the (v)MSRs and expect it to work.