diff mbox series

[kvm-unit-tests,15/39] x86/access: Preserve A/D bits when writing paging structure entries

Message ID 20211125012857.508243-16-seanjc@google.com (mailing list archive)
State New, archived
Headers show
Series x86/access: nVMX: Big overhaul | expand

Commit Message

Sean Christopherson Nov. 25, 2021, 1:28 a.m. UTC 
Preserve A/D bits for paging structure entries to avoid pointless writes
to PTEs between test iterations, and more importantly to avoid triggering
MMU syncs due to writing upper-level PTEs.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 x86/access.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/x86/access.c b/x86/access.c
index 53b1221..c4db368 100644
--- a/x86/access.c
+++ b/x86/access.c
@@ -609,7 +609,11 @@  static pt_element_t ac_get_pt(ac_test_t *at, int i, pt_element_t *ptep)
 		abort();
 	}
 
-	pte = at->page_tables[i];
+	/*
+	 * Preserve A/D bits to avoid writing upper level PTEs,
+	 * which cannot be unsyc'd when KVM uses shadow paging.
+	 */
+	pte = at->page_tables[i] | (pte & (PT_DIRTY_MASK | PT_ACCESSED_MASK));
 	return pte;
 }