[PATCH 4/6] KVM: Documentation: Add the missing tdp_mmu_root_count into kvm_mmu_page

[Mingwei Zhang <mizhang@google.com>]

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@google.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
+    accesses.  Accessing the page requires lifting the counter value. The
+    initial value is set as 2 indicating one reference from vCPU and one
+    from TDP MMU itself. While this counter is nonzero, the page cannot be
+    destroyed. Note this field is a union with root_count.
   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
-- 
2.41.0.162.gfafddb0af9-goog