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

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Message-ID: <87sfo7igis.fsf@redhat.com>
Date:   Tue, 14 Jun 2022 14:19:39 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     mail@...rudhrb.com, kumarpraveen@...ux.microsoft.com,
        Anirudh Rayabharam <anrayabh@...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

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

...

>
> As per the comments in arch/x86/kvm/vmx/evmcs.h, TSC multiplier field is
> currently not supported in EVMCS.

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


View attachment "0001-KVM-x86-Allow-some-previously-forbidden-controls-whe.patch" of type "text/x-patch" (5548 bytes)