linux-kernel - Re: [PATCH] KVM: nVMX: Don't expose TSC scaling to L1 when on Hyper-V

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Message-ID: <87k098y77x.fsf@redhat.com>
Date:   Wed, 22 Jun 2022 18:48:50 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.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>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Ilias Stamatis <ilstam@...zon.com>,
        Maxim Levitsky <mlevitsk@...hat.com>, mail@...rudhrb.com,
        kumarpraveen@...ux.microsoft.com, wei.liu@...nel.org,
        robert.bradford@...el.com, liuwe@...rosoft.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: Don't expose TSC scaling to L1 when on Hyper-V

Anirudh Rayabharam <anrayabh@...ux.microsoft.com> writes:

> On Wed, Jun 22, 2022 at 04:35:27PM +0200, Vitaly Kuznetsov wrote:

...

>> 
>> I've tried to pick it up but it's actually much harder than I think. The
>> patch has some minor issues ('&vmcs_config.nested' needs to be switched
>> to '&vmcs_conf->nested' in nested_vmx_setup_ctls_msrs()), but the main
>> problem is that the set of controls nested_vmx_setup_ctls_msrs() needs
>> is NOT a subset of vmcs_config (setup_vmcs_config()). I was able to
>> identify at least:

...

I've jsut sent "[PATCH RFC v1 00/10] KVM: nVMX: Use vmcs_config for
setting up nested VMX MSRs" which implements Sean's suggestion. Hope
this is the way to go for mainline.

>
> How about we do something simple like the patch below to start with?
> This will easily apply to stable and we can continue improving upon
> it with follow up patches on mainline.
>

Personally, I'm not against this for @stable. Alternatively, in case the
only observed issue is with TSC scaling, we can add support for it for
KVM-on-Hyper-V but not for Hyper-V-on-KVM (a small subset of "[PATCH
00/11] KVM: VMX: Support TscScaling and EnclsExitingBitmap whith
eVMCS"). I can prepare patches if needed.

-- 
Vitaly