From: Jim Mattson <jmattson@google.com>
To: Like Xu <like.xu.linux@gmail.com>
Cc: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v2 1/3] KVM: x86/pmu: Stop adding speculative Intel GP PMCs that don't exist yet
Date: Wed, 7 Sep 2022 09:33:13 -0700 [thread overview]
Message-ID: <CALMp9eSPfxPunKW-K6LLPxsXdaeezKU=2G9Sdh7FS6VGb3goFA@mail.gmail.com> (raw)
In-Reply-To: <20220907104838.8424-1-likexu@tencent.com>
On Wed, Sep 7, 2022 at 3:48 AM Like Xu <like.xu.linux@gmail.com> wrote:
>
> From: Like Xu <likexu@tencent.com>
>
> The Intel April 2022 SDM - Table 2-2. IA-32 Architectural MSRs adds
> a new architectural IA32_OVERCLOCKING_STATUS msr (0x195), plus the
> presence of IA32_CORE_CAPABILITIES (0xCF), the theoretical effective
> maximum value of the Intel GP PMCs is 14 (0xCF - 0xC1) instead of 18.
>
> But the conclusion of this speculation "14" is very fragile and can
> easily be overturned once Intel declares another meaningful arch msr
> in the above reserved range, and even worse, Intel probably put PMCs
> 8-15 in a completely different range of MSR indices.
The last clause is just conjecture.
> A conservative proposal would be to stop at the maximum number of Intel
> GP PMCs supported today. Also subsequent changes would limit both AMD
> and Intel on the number of GP counter supported by KVM.
>
> There are some boxes like Intel P4 may indeed have 18 counters, but
> those counters are in a completely different msr address range and do
> not strictly adhere to the Intel Arch PMU specification, and will not
> be supported by KVM in the near future.
The P4 PMU isn't virtualized by KVM today, is it?
>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Suggested-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Like Xu <likexu@tencent.com>
Please put the "Fixes" tag back. You convinced me that it should be there.
Reviewed-by: Jim Mattson <jmattson@google.com>
next prev parent reply other threads:[~2022-09-07 16:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-07 10:48 [PATCH v2 1/3] KVM: x86/pmu: Stop adding speculative Intel GP PMCs that don't exist yet Like Xu
2022-09-07 10:48 ` [PATCH v2 2/3] KVM: x86/pmu: Limit the maximum number of supported Intel GP counters Like Xu
2022-09-07 16:29 ` Jim Mattson
2022-09-07 10:48 ` [PATCH v2 3/3] KVM: x86/pmu: Limit the maximum number of supported AMD " Like Xu
2022-09-07 16:33 ` Jim Mattson [this message]
2022-09-19 8:49 ` [PATCH v2 1/3] KVM: x86/pmu: Stop adding speculative Intel GP PMCs that don't exist yet Like Xu
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