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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Anirudh Rayabharam <anrayabh@linux.microsoft.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     mail@anirudhrb.com, kumarpraveen@linux.microsoft.com,
        wei.liu@kernel.org, robert.bradford@intel.com, liuwe@microsoft.com,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Ilias Stamatis <ilstam@amazon.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH] KVM: nVMX: Don't expose TSC scaling to L1 when on Hyper-V
In-Reply-To: <Yqmf5UGbNKyGz3dD@anrayabh-desk>
References: <20220613161611.3567556-1-anrayabh@linux.microsoft.com>
 <87sfo7igis.fsf@redhat.com>
 <eaefdea0-0ca3-93f1-a815-03900055fdcd@redhat.com>
 <Yqmf5UGbNKyGz3dD@anrayabh-desk>
Date:   Wed, 15 Jun 2022 11:36:56 +0200
Message-ID: <87mteei7yf.fsf@redhat.com>
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Anirudh Rayabharam <anrayabh@linux.microsoft.com> writes:

> On Tue, Jun 14, 2022 at 07:20:34PM +0200, Paolo Bonzini wrote:
>> On 6/14/22 14:19, Vitaly Kuznetsov wrote:
>> > The latest version:
>> > https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/datatypes/hv_vmx_enlightened_vmcs
>> > 
>> > has it, actually. It was missing before (compare with e.g. 6.0b version
>> > here:
>> > https://github.com/MicrosoftDocs/Virtualization-Documentation/raw/live/tlfs/Hypervisor%20Top%20Level%20Functional%20Specification%20v6.0b.pdf)
>> > 
>> > but AFAIR TSC scaling wasn't advertised by genuine Hyper-V either.
>> > Interestingly enough, eVMCS version didn't change when these fields were
>> > added, it is still '1'.
>> > 
>> > I even have a patch in my stash (attached). I didn't send it out because
>> > it wasn't properly tested with different Hyper-V versions.
>> > 
>> > -- Vitaly
>> 
>> Anirudh, can you check if Vitaly's patches work for you?
>
> I will check it. But I wonder if they fit the criteria for inclusion in
> stable trees...
>
> It is important for the fix to land in the stable trees since this issue
> is a regression that was introduced _after_ 5.13. (I probably should've
> mentioned this in the changelog.)
>

Personally, I see no problem with splitting off TscMultiplier part from
my patch and marking it for stable@ fixing d041b5ea93352. I'm going to
run some tests too.

-- 
Vitaly