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

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Date:   Mon, 22 Aug 2022 14:51:52 +0000
From:   Andrew Cooper <Andrew.Cooper3@...rix.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Liang, Kan" <kan.liang@...ux.intel.com>
CC:     "acme@...hat.com" <acme@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        Jianfeng Gao <jianfeng.gao@...el.com>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>
Subject: Re: [RESEND PATCH] perf/x86/intel: Fix unchecked MSR access error for
 Alder Lake N

On 22/08/2022 15:39, Peter Zijlstra wrote:
> 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 about this?

LGTM.

It's not even just uarch problems.  There are arch problems too, like
the fact that P and E cores disagree on linear vs effective addresses,
number of counters, etc.

~Andrew