linux-kernel - Re: [PATCH] KVM: nVMX: Dynamically compute max VMCS index for vmcs12

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Message-ID: <c847e00a-e422-cdc9-3317-fbbd82b6e418@redhat.com>
Date:   Mon, 21 Jun 2021 18:39:04 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: Dynamically compute max VMCS index for vmcs12

On 18/06/21 23:46, Sean Christopherson wrote:
> Calculate the max VMCS index for vmcs12 by walking the array to find the
> actual max index.  Hardcoding the index is prone to bitrot, and the
> calculation is only done on KVM bringup (albeit on every CPU, but there
> aren't _that_ many null entries in the array).
> 
> Fixes: 3c0f99366e34 ("KVM: nVMX: Add a TSC multiplier field in VMCS12")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
> 
> Note, the vmx test in kvm-unit-tests will still fail using stock QEMU,
> as QEMU also hardcodes and overwrites the MSR.  The test passes if I
> hack KVM to ignore userspace (it was easier than rebuilding QEMU).

Queued, thanks.  Without having checked the kvm-unit-tests sources very 
thoroughly, this might be a configuration issue in kvm-unit-tests; in 
theory "-cpu host" (unlike "-cpu host,migratable=no") should not enable 
TSC scaling.

Paolo