On Mon, Jun 26, 2023, Mingwei Zhang wrote:
> Add the missing description for ptep in kvm_mmu_page description. ptep is
> used when TDP MMU is enabled and it shares the storage with parent_ptes.
> Update the doc to help readers to get up-to-date info.
>
> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> ---
> Documentation/virt/kvm/x86/mmu.rst | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
> index 4c9044b4dc6c..5cd6cd5e8926 100644
> --- a/Documentation/virt/kvm/x86/mmu.rst
> +++ b/Documentation/virt/kvm/x86/mmu.rst
> @@ -237,6 +237,11 @@ Shadow pages contain the following information:
> parent_ptes points at this single spte, otherwise, there exists multiple
> sptes pointing at this page and (parent_ptes & ~0x1) points at a data
> structure with a list of parent sptes.
> + ptep:
> + The reverse mapping for the pte pointing at this page's spt. This field is
I don't think describing "reverse mapping" is necessary, and it's arguably even
misleading. A "reverse mapping" typically provides a way to find mappings given
a (guest) physical address. The TDP MMU doesn't bother with reverse mappings
because there is exactly one possible mapping for any given gfn. The "ptep" exists
specifically to expedite zapping a single TDP MMU shadow page, i.e. allows zapping
without having to traverse the paging tree.
The ptep field is just a pointer at the SPTE, no more no less. Something like
this?
ptep:
The kernel virtual address of the SPTE that points at this shadow page.
Used exclusively by the TDP MMU, this field is a union with parent_ptes.
> + used in replace of parent_ptes when TDP MMU is used. In TDP MMU, each
> + non-root shadow page will have one parent, while each root shadow page has
> + no parent. Note that this field is a union with parent_ptes.
> unsync:
> If true, then the translations in this page may not match the guest's
> translation. This is equivalent to the state of the tlb when a pte is
> --
> 2.41.0.162.gfafddb0af9-goog
>
