[v4,4/6] KVM: Documentation: Add the missing description for tdp_mmu_root_count into kvm_mmu_page

Commit Message

Mingwei Zhang Sept. 12, 2023, 6:45 p.m. UTC

Add the description of tdp_mmu_root_count into kvm_mmu_page description and
combine it with the description of root_count. tdp_mmu_root_count is an
atomic counter used only in TDP MMU. Update the doc.

Signed-off-by: Mingwei Zhang <[e-mail]>
Reviewed-by: Kai Huang <[e-mail]>
---
 Documentation/virt/kvm/x86/mmu.rst | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

Patch

diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
index 22d221c180d7..4a82fa016833 100644
--- a/Documentation/virt/kvm/x86/mmu.rst
+++ b/Documentation/virt/kvm/x86/mmu.rst
@@ -229,10 +229,13 @@  Shadow pages contain the following information:
     can be calculated from the gfn field when used.  In addition, when
     role.direct is set, KVM does not track access permission for each of the
     gfn. See role.direct and gfn.
-  root_count:
-    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.
+  root_count / tdp_mmu_root_count:
+     root_count is a reference counter for root shadow pages in Shadow MMU.
+     vCPUs elevate the refcount when getting a shadow page that will be used as
+     a root page, i.e. page that will be loaded into hardware directly (CR3,
+     PDPTRs, nCR3 EPTP). Root pages cannot be destroyed while their refcount is
+     non-zero. See role.invalid. tdp_mmu_root_count is similar but exclusively
+     used in TDP MMU as an atomic refcount.
   parent_ptes:
     The reverse mapping for the pte/ptes pointing at this page's spt. If
     parent_ptes bit 0 is zero, only one spte points at this page and