linux-kernel - Re: [PATCH v2] KVM: x86/pmu: Fix emulation on Intel counters' bit width

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Message-ID: <CABgObfYfiUDf4zY=izcg_32yGCbUxxVc+JAkHGHwiQ0VmGdOgA@mail.gmail.com>
Date:   Mon, 27 Mar 2023 16:30:08 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86/pmu: Fix emulation on Intel counters' bit width

On Wed, Mar 22, 2023 at 10:31 AM Like Xu <like.xu.linux@...il.com> wrote:
>
> From: Like Xu <likexu@...cent.com>
>
> Per Intel SDM, the bit width of a PMU counter is specified via CPUID
> only if the vCPU has FW_WRITE[bit 13] on IA32_PERF_CAPABILITIES.
> When the FW_WRITE bit is not set, only EAX is valid and out-of-bounds
> bits accesses do not generate #GP. Conversely when this bit is set, #GP
> for out-of-bounds bits accesses will also appear on the fixed counters.
> vPMU currently does not support emulation of bit widths lower than 32
> bits or higher than its host capability.

Can you please point out the date and paragraph of the SDM?

Paolo