| Message ID | 20230626182016.4127366-4-mizhang@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Update document description for kvm_mmu_page and kvm_mmu_page_role | expand |
On 6/26/23 11:20, 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@google.com> > --- > 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 > + used in replace of parent_ptes when TDP MMU is used. In TDP MMU, each in replacement of > + 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
On Mon, 2023-06-26 at 18:20 +0000, 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@google.com> > --- > 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 > + 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 > Reviewed-by: Kai Huang <kai.huang@intel.com>
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@google.com> > --- > 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 >
On Tue, Jun 27, 2023, Sean Christopherson wrote: > 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@google.com> > > --- > > 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. > Sure, I can this version instead. Technically, it is still a reverse mapping, but yeah, I agree that introducing this one is confusing. > > + 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 > >
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 + 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
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@google.com> --- Documentation/virt/kvm/x86/mmu.rst | 5 +++++ 1 file changed, 5 insertions(+)