linux-kernel - Re: [PATCH v9 3/6] KVM: x86: Virtualize CR3.LAM

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Date:   Fri, 21 Jul 2023 18:28:23 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, chao.gao@...el.com, kai.huang@...el.com,
        David.Laight@...lab.com, robert.hu@...ux.intel.com
Subject: Re: [PATCH v9 3/6] KVM: x86: Virtualize CR3.LAM_{U48,U57}

On Mon, Jul 03, 2023, Binbin Wu wrote:
> 
> On 6/29/2023 1:40 AM, Sean Christopherson wrote:
> > On Wed, Jun 28, 2023, Binbin Wu wrote:
> > > 
> > > On 6/28/2023 7:40 AM, Sean Christopherson wrote:
> > > > I think I'd prefer to drop this field and avoid bikeshedding the name entirely.  The
> > > > only reason to effectively cache "X86_CR3_LAM_U48 | X86_CR3_LAM_U57" is because
> > > > guest_cpuid_has() is slow, and I'd rather solve that problem with the "governed
> > > > feature" framework.
> > > Thanks for the suggestion.
> > > 
> > > Is the below patch the lastest patch of "governed feature" framework
> > > support?
> > > https://lore.kernel.org/kvm/20230217231022.816138-2-seanjc@google.com/
> > Yes, I haven't refreshed it since the original posting.
> > 
> > > Do you have plan to apply it to kvm-x86 repo?
> > I'm leaning more and more towards pushing it through sooner than later as this
> > isn't the first time in recent memory that a patch/series has done somewhat odd
> > things to workaround guest_cpuid_has() being slow.  I was hoping to get feedback
> > before applying, but that's not looking likely at this point.
> Hi Sean,
> 
> I plan to adopt the "KVM-governed feature framework" to track whether the
> guest can use LAM feature.
> Because your patchset is not applied yet, there are two ways to do it. Which
> one do you prefer?
> 
> Option 1:
> Make KVM LAM patchset base on your "KVM-governed feature framework"
> patchset.
> 
> Option 2:
> Temporarily add a bool in kvm_vcpu_arch as following, and use the bool
> "can_use_lam" instead of guest_can_use(vcpu, X86_FEATURE_LAM).
> And provide a cleanup patch to use "KVM-governed feature framework", which
> can be applied along with or after your patchset.

Sorry for not responding.  I was hoping I could get v2 posted before advising on
a direction, but long story short, I made a few goofs and got delayed (I won't get
v2 out until next week).  Belatedly, either option is fine by me (I see you posted
v10 on top of the governed feature stuff).

Thank!  And again, sorry.