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

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Message-ID: <87bkujy4z9.fsf@redhat.com>
Date:   Thu, 23 Jun 2022 13:49:30 +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 06:48:50PM +0200, Vitaly Kuznetsov wrote:
>> 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
>
> I think it's a good intermediate fix for mainline too. It is easier to land
> it in stable if it already exists in mainline. It can stay in mainline
> until your series lands and replaces it with the vmcs_config approach.
>
> What do you think?
>

Paolo's call but personally I think both series can make 5.20 so there's
no need for an intermediate solution.

>> 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.
>
> Will it fit in stable's 100 line rule?
>

Yes, please take a look at the attached patches (5.18.y based). First 3
are identical to what I've sent for mainline, the last one is reduced to
only support TSC scaling for KVM on Hyper-V (but not Hyper-V on
KVM). Compile tested only, proceed with caution)

-- 
Vitaly


View attachment "0001-x86-hyperv-Fix-struct-hv_enlightened_vmcs-definition.patch" of type "text/x-patch" (2147 bytes)

View attachment "0002-x86-hyperv-Update-struct-hv_enlightened_vmcs-definit.patch" of type "text/x-patch" (1559 bytes)

View attachment "0003-KVM-VMX-Define-VMCS-to-EVMCS-conversion-for-the-new-.patch" of type "text/x-patch" (3126 bytes)

View attachment "0004-KVM-VMX-Support-TSC-scaling-with-enlightened-VMCS.patch" of type "text/x-patch" (3319 bytes)