linux-kernel - Re: [PATCH v2 6/6] KVM: Documentation: Add the missing description for tdp_mmu_page into kvm_mmu

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Message-ID: <ZJsLV+urA0Yrw6Wn@google.com>
Date:   Tue, 27 Jun 2023 09:16:23 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Mingwei Zhang <mizhang@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kai Huang <kai.huang@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>, Xu Yilun <yilun.xu@...el.com>,
        Zhi Wang <zhi.wang.linux@...il.com>
Subject: Re: [PATCH v2 6/6] KVM: Documentation: Add the missing description
 for tdp_mmu_page into kvm_mmu_page

On Mon, Jun 26, 2023, Mingwei Zhang wrote:
> Add the description for tdp_mmu_page into kvm_mmu_page description.
> tdp_mmu_page is a field to differentiate shadow pages from TDP MMU and
> non-TDP MMU. When TDP MMU is enabled, sp->tdp_mmu_page=1 indicates a shadow
> page for L1, while sp->tdp_mmu_page=0 indicates a shadow page for an L2.
> When TDP MMU is disabled, sp->tdp_mmu_page is always 0. So update the doc
> to reflect the information.
> 
> Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
> ---
>  Documentation/virt/kvm/x86/mmu.rst | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
> index cc4bd190c93d..678dc0260a54 100644
> --- a/Documentation/virt/kvm/x86/mmu.rst
> +++ b/Documentation/virt/kvm/x86/mmu.rst
> @@ -278,6 +278,8 @@ Shadow pages contain the following information:
>      since the last time the page table was actually used; if emulation
>      is triggered too frequently on this page, KVM will unmap the page
>      to avoid emulation in the future.
> +  tdp_mmu_page:
> +    Is 1 if the shadow page is a TDP MMU page.

Maybe add a short blurb explaining that it's used for control flow when starting
from a common entry point?  E.g. walking page tables given a root, and walking
lists that can hold both shadow MMU and TDP MMU pages.