linux-kernel - Re: [PATCH v5 01/26] KVM: x86: hyper-v: Expose access to debug MSRs in the partition privilege flags

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Message-ID: <Yv5fcKOEVAlAh0px@google.com>
Date:   Thu, 18 Aug 2022 15:49:04 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/26] KVM: x86: hyper-v: Expose access to debug MSRs
 in the partition privilege flags

On Thu, Aug 18, 2022, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@...gle.com> writes:
> 
> > On Tue, Aug 02, 2022, Vitaly Kuznetsov wrote:
> >> For some features, Hyper-V spec defines two separate CPUID bits: one
> >> listing whether the feature is supported or not and another one showing
> >> whether guest partition was granted access to the feature ("partition
> >> privilege mask"). 'Debug MSRs available' is one of such features. Add
> >> the missing 'access' bit.
> >> 
> >> Note: hv_check_msr_access() deliberately keeps checking
> >> HV_FEATURE_DEBUG_MSRS_AVAILABLE bit instead of the new HV_ACCESS_DEBUG_MSRS
> >> to not break existing VMMs (QEMU) which only expose one bit. Normally, VMMs
> >> should set either both these bits or none.
> >
> > This is not the right approach long term.  If KVM absolutely cannot unconditionally
> > switch to checking HV_ACCESS_DEBUG_MSRS because it would break QEMU users, then we
> > should add a quirk, but sweeping the whole thing under the rug is wrong.
> >
> 
> First, this patch is kind of unrelated to the series so in case it's the
> only thing which blocks it from being merged -- let's just pull it out
> and discuss separately.

Regarding the series, are there any true dependencies between the eVMCS patches
(1 - 11) and the VMCS sanitization rework (12 - 26)?  I.e. can the VMCS rework
be queued ahead of the eVMCS v1 support?