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 <mizhang@xxxxxxxxxx>
Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
---
Documentation/virt/kvm/x86/mmu.rst | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
index 17d90974204e..40daf8beb9b1 100644
--- a/Documentation/virt/kvm/x86/mmu.rst
+++ b/Documentation/virt/kvm/x86/mmu.rst
@@ -229,10 +229,14 @@ 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. When the value is non-zero, it
+ allows vCPUs acquire references while holding mmu_lock for read.
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
--
2.41.0.585.gd2178a4bd4-goog
