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

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Message-ID: <YrrYMHbiO0UuLZYN@anrayabh-desk>
Date:   Tue, 28 Jun 2022 16:00:08 +0530
From:   Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        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

On Thu, Jun 23, 2022 at 01:49:30PM +0200, Vitaly Kuznetsov wrote:
> Anirudh Rayabharam <anrayabh@...ux.microsoft.com> writes:
> 
> > On Wed, Jun 22, 2022 at 06:48:50PM +0200, Vitaly Kuznetsov wrote:
> >> Anirudh Rayabharam <anrayabh@...ux.microsoft.com> 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 reason I see for this intermediate solution is to automatically
land the fix in stable without bothering to write a special backport.

I will send it as a proper patch and see if there is any interest in
taking it.

	- Anirudh.