linux-kernel - Re: [PATCH 4/6] KVM: Documentation: Add the missing tdp_mmu_root_count into kvm_mmu

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Message-ID: <ZJnQ9w5deFHhElu9@google.com>
Date:   Mon, 26 Jun 2023 17:55:03 +0000
From:   Mingwei Zhang <mizhang@...gle.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "bgardon@...gle.com" <bgardon@...gle.com>
Subject: Re: [PATCH 4/6] KVM: Documentation: Add the missing
 tdp_mmu_root_count into kvm_mmu_page

On Thu, Jun 22, 2023, Huang, Kai wrote:
> On Sun, 2023-06-18 at 00:08 +0000, Mingwei Zhang wrote:
> > Add tdp_mmu_root_count into kvm_mmu_page description. tdp_mmu_root_count is
> > an atomic counter used only in TDP MMU. Its usage and meaning is slightly
> > different with root_counter in shadow MMU. Update the doc.
> > 
> > Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
> > ---
> >  Documentation/virt/kvm/x86/mmu.rst | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
> > index 36bfe0fe02bb..3dce2426ad6d 100644
> > --- a/Documentation/virt/kvm/x86/mmu.rst
> > +++ b/Documentation/virt/kvm/x86/mmu.rst
> > @@ -230,6 +230,12 @@ Shadow pages contain the following information:
> >      A counter keeping track of how many hardware registers (guest cr3 or
> >      pdptrs) are now pointing at the page.  While this counter is nonzero, the
> >      page cannot be destroyed.  See role.invalid.
> > +  tdp_mmu_root_count:
> > +    An atomic reference counter in TDP MMU that allows for parallel
> 					     ^
> Please explicitly say "TDP MMU root page" ?
>
> > +    accesses.  Accessing the page requires lifting the counter value. The
> > +    initial value is set as 2 indicating one reference from vCPU and one
> 			    ^
> 			    to ?
> 
> > +    from TDP MMU itself. 
> > 
> 
> 
> > While this counter is nonzero, the page cannot be
> > +    destroyed. 
> > 
> 
> I guess this sentence is implied by "reference counter" mentioned in the first
> sentence.
> 

Will make the changes in next version.

-Mingwei