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

[Vitaly Kuznetsov]

 Anirudh Rayabharam <anrayabh@xxxxxxxxxxxxxxxxxxx> writes:

> On Wed, Jun 22, 2022 at 06:48:50PM +0200, Vitaly Kuznetsov wrote:
>> Anirudh Rayabharam <anrayabh@xxxxxxxxxxxxxxxxxxx> 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