linux-kernel - Re: [PATCH v4 3/3] KVM: selftests: Test behavior of KVM_X86_DISABLE_EXITS

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Message-ID: <2e32978a-25c4-45a9-bdff-3097bb3abcdd@linux.intel.com>
Date: Wed, 11 Jun 2025 09:47:04 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Jim Mattson <jmattson@...gle.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v4 3/3] KVM: selftests: Test behavior of
 KVM_X86_DISABLE_EXITS_APERFMPERF


On 6/11/2025 12:59 AM, Jim Mattson wrote:
> On Tue, Jun 10, 2025 at 1:42 AM Mi, Dapeng <dapeng1.mi@...ux.intel.com> wrote:
>>
>> On 5/31/2025 2:52 AM, Jim Mattson wrote:
>>> For a VCPU thread pinned to a single LPU, verify that interleaved host
>>> and guest reads of IA32_[AM]PERF return strictly increasing values when
>>> APERFMPERF exiting is disabled.
>> Should we consider the possible overflow case of these 2 MSRs although it
>> could be extremely rare? Thanks.
> Unless someone moves the MSRs forward, at current frequencies, the
> machine will have to be up for more than 100 years. I'll be long dead
> by then.

😂


>
> Note that frequency invariant scheduling doesn't accommodate overflow
> either. If the MSRs overflow, frequency invariant scheduling is
> disabled.
Agree.