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

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Message-ID: <Yqmf5UGbNKyGz3dD@anrayabh-desk>
Date:   Wed, 15 Jun 2022 14:31:25 +0530
From:   Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...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,
        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>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH] KVM: nVMX: Don't expose TSC scaling to L1 when on Hyper-V

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.)

Thanks,

	Anirudh.

> 
> Paolo