linux-kernel - Re: [PATCH v4] KVM: x86: Fix KVM_GET_CPUID2 ioctl to return cpuid entries count

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Message-ID: <514b5373-c07b-ad34-5fba-f8850faf6d68@redhat.com>
Date:   Tue, 4 May 2021 10:21:47 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Denis V. Lunev" <den@...nvz.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Valeriy Vdovin <valeriy.vdovin@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Shuah Khan <shuah@...nel.org>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Alexander Graf <graf@...zon.com>,
        Andrew Jones <drjones@...hat.com>,
        Oliver Upton <oupton@...gle.com>,
        Like Xu <like.xu@...ux.intel.com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4] KVM: x86: Fix KVM_GET_CPUID2 ioctl to return cpuid
 entries count

On 04/05/21 10:15, Denis V. Lunev wrote:
> As far as I understand only some testing within kernel now.
> Though we have plans to expose it for QAPI as the series
> in QEMU
>    [PATCH 1/2] qapi: fix error handling for x-vz-query-cpu-model-cpuid
>    [PATCH 2/2] qapi: blacklisted x-vz-query-cpu-model-cpuid in tests
> is not coming in a good way.
> The idea was to avoid manual code rework in QEMU and
> expose collected model at least for debug.

KVM_GET_CPUID2 as a VM ioctl cannot expose the whole truth about CPUID 
either, since it doesn't handle the TSX_CTRL_CPUID_CLEAR bit.  Given 
that QEMU doesn't need KVM_GET_CPUID2; it only needs to save whatever it 
passed to KVM_SET_CPUID2.

Paolo