linux-kernel - Re: [PATCH RFC] Revert "KVM: VMX: Micro-optimize vmexit time when not exposing PMU"

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Message-ID: <87366rguot.fsf@vitty.brq.redhat.com>
Date:   Fri, 19 Jun 2020 13:29:38 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     like.xu@...el.com, kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>,
        Maxime Coquelin <maxime.coquelin@...hat.com>,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH RFC] Revert "KVM: VMX: Micro-optimize vmexit time when not exposing PMU"

"Xu, Like" <like.xu@...el.com> writes:

> On 2020/6/19 17:40, Vitaly Kuznetsov wrote:
>> Guest crashes are observed on a Cascade Lake system when 'perf top' is
>> launched on the host, e.g.
> Interesting, is it specific to Cascade Lake?
>

Actually no, just reproduced this on a Haswell system. If you run the
guest with "-cpu host,-pmu" and do 'perf top' (on the host) the guest
crashes immediately.

> Would you mind sharing the output of
> "cpuid -r -l 1 -1" and "cat /proc/cpuinfo| grep microcode | uniq" with us ?

Sure (this is probably unrelated because the issue also reproduces on
Haswell but still):

# cpuid -r -l 1 -1

CPU:
   0x00000001 0x00: eax=0x00050657 ebx=0x03200800 ecx=0x7ffefbff edx=0xbfebfbff

# cat /proc/cpuinfo| grep microcode | uniq
microcode	: 0x500002c

This is "Intel(R) Xeon(R) Gold 5218 CPU @ 2.30GHz"

-- 
Vitaly