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[14/24] KVM: x86/mmu: Document dependency bewteen TDP A/D type and saved bits

Message ID 20210225204749.1512652-15-seanjc@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86/mmu: Introduce MMU_PRESENT and fix bugs | expand

Commit Message

Sean Christopherson Feb. 25, 2021, 8:47 p.m. UTC
Document that SHADOW_ACC_TRACK_SAVED_BITS_SHIFT is directly dependent on
bits 53:52 being used to track the A/D type.

Remove PT64_SECOND_AVAIL_BITS_SHIFT as it is at best misleading, and at
worst wrong.  For PAE paging, which arguably is a variant of PT64, the
bits are reserved.  For MMIO SPTEs the bits are not available as they're
used for the MMIO generation.  For access tracked SPTEs, they are also
not available as bits 56:54 are used to store the original RX bits.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
 arch/x86/kvm/mmu/spte.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)
diff mbox series


diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index bf4f49890606..e918b8f0b21d 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -6,7 +6,6 @@ 
 #include "mmu_internal.h"
  * TDP SPTES (more specifically, EPT SPTEs) may not have A/D bits, and may also
@@ -134,11 +133,14 @@  extern u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
  * The mask/shift to use for saving the original R/X bits when marking the PTE
  * as not-present for access tracking purposes. We do not save the W bit as the
  * PTEs being access tracked also need to be dirty tracked, so the W bit will be
- * restored only when a write is attempted to the page.
+ * restored only when a write is attempted to the page.  This mask obviously
+ * must not overlap the A/D type mask.
  * If a thread running without exclusive control of the MMU lock must perform a