[kvm-unit-tests PATCH 16/39] x86/access: Make toggling of PRESENT bit a "higher order" action

[Sean Christopherson <seanjc@google.com>]

Make the PRESENT bit a higher order bit so that it isn't toggled on every
iteration, which is a wee bit problematic when trying to expose bugs in
KVM's TLB flushing since a fault is architecturally guaranteed to flush
TLB entries for the faulting virtual address.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 x86/access.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/x86/access.c b/x86/access.c
index c4db368..24ddeec 100644
--- a/x86/access.c
+++ b/x86/access.c
@@ -37,26 +37,30 @@ static int invalid_mask;
 	  (((address) >> (12 + ((level)-1) * 9)) & 511)
 
 /*
- * page table access check tests
+ * Page table access check tests.  Each number/bit represent an individual
+ * test case.  The main test will bump a counter by 1 to run all permutations
+ * of the below test cases (sans illegal combinations).
+ *
+ * Keep the PRESENT and reserved bits in the higher numbers so that they aren't
+ * toggled on every test, e.g. to keep entries in the TLB.
  */
-
 enum {
-	AC_PTE_PRESENT_BIT,
 	AC_PTE_WRITABLE_BIT,
 	AC_PTE_USER_BIT,
 	AC_PTE_ACCESSED_BIT,
 	AC_PTE_DIRTY_BIT,
 	AC_PTE_NX_BIT,
+	AC_PTE_PRESENT_BIT,
 	AC_PTE_BIT51_BIT,
 	AC_PTE_BIT36_BIT,
 
-	AC_PDE_PRESENT_BIT,
 	AC_PDE_WRITABLE_BIT,
 	AC_PDE_USER_BIT,
 	AC_PDE_ACCESSED_BIT,
 	AC_PDE_DIRTY_BIT,
 	AC_PDE_PSE_BIT,
 	AC_PDE_NX_BIT,
+	AC_PDE_PRESENT_BIT,
 	AC_PDE_BIT51_BIT,
 	AC_PDE_BIT36_BIT,
 	AC_PDE_BIT13_BIT,
-- 
2.34.0.rc2.393.gf8c9666880-goog