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

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Date:   Wed, 22 Jun 2022 10:00:29 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
Cc:     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

Sean Christopherson <seanjc@...gle.com> writes:

> On Tue, Jun 14, 2022, Anirudh Rayabharam wrote:
>> On Mon, Jun 13, 2022 at 04:57:49PM +0000, Sean Christopherson wrote:

...

>> > 
>> > Any reason not to use the already sanitized vmcs_config?  I can't think of any
>> > reason why the nested path should blindly use the raw MSR values from hardware.
>> 
>> vmcs_config has the sanitized exec controls. But how do we construct MSR
>> values using them?
>
> I was thinking we could use the sanitized controls for the allowed-1 bits, and then
> take the required-1 bits from the CPU.  And then if we wanted to avoid the redundant
> RDMSRs in a follow-up patch we could add required-1 fields to vmcs_config.
>
> Hastily constructed and compile-tested only, proceed with caution :-)

Independently from "[PATCH 00/11] KVM: VMX: Support TscScaling and
EnclsExitingBitmap whith eVMCS" which is supposed to fix the particular
TSC scaling issue, I like the idea to make nested_vmx_setup_ctls_msrs()
use both allowed-1 and required-1 bits from vmcs_config. I'll pick up
the suggested patch and try to construct something for required-1 bits.

Thanks!

-- 
Vitaly