linux-kernel - Re: [PATCH 05/12] KVM: x86: Use KVM-governed feature framework to track "XSAVES enabled"

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Message-ID: <20230224095409.bo77lwb6wbsc53hx@linux.intel.com>
Date:   Fri, 24 Feb 2023 17:54:09 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/12] KVM: x86: Use KVM-governed feature framework to
 track "XSAVES enabled"

On Wed, Feb 22, 2023 at 10:56:04AM -0800, Sean Christopherson wrote:
> On Tue, Feb 21, 2023, Yu Zhang wrote:
> > On Fri, Feb 17, 2023 at 03:10:15PM -0800, Sean Christopherson wrote:
> > > Use the governed feature framework to track if XSAVES is "enabled", i.e.
> > > if XSAVES can be used by the guest.  Add a comment in the SVM code to
> > > explain the very unintuitive logic of deliberately NOT checking if XSAVES
> > > is enumerated in the guest CPUID model.
> > > 
> > > No functional change intended.
> > 
> > xsaves_enabled in struct kvm_vcpu_arch is no longer used. But instead of
> > just deleting it, maybe we could move 'bool load_eoi_exitmap_pending' to
> > its place, so 7 bytes can be saved for each struct kvm_vcpu_arch:
> 
> I prefer leaving load_eoi_exitmap_pending where it is so that it's co-located with
> ioapic_handled_vectors.  I agree wasting 7 bytes is unfortunate, but I don't want
> to take an ad hoc approach to shrinking per-vCPU structs.  See the link below for
> more discussion.
> 
> https://lore.kernel.org/all/20230213163351.30704-1-minipli@grsecurity.net

Fair enough. :)

Thanks
Yu