KVM: x86: assign two bits to track SPTE kinds

Currently, we are overloading SPTE_SPECIAL_MASK to mean both
"A/D bits unavailable" and MMIO, where the difference between the
two is determined by mio_mask and mmio_value.

However, the next patch will need two bits to distinguish
availability of A/D bits from write protection.  So, while at
it give MMIO its own bit pattern, and move the two bits from
bit 62 to bits 52..53 since Intel is allocating EPT page table
bits from the top.
Reviewed-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -219,13 +219,6 @@ enum {
 				 PFERR_WRITE_MASK |		\
 				 PFERR_PRESENT_MASK)
 
-/*
- * The mask used to denote special SPTEs, which can be either MMIO SPTEs or
- * Access Tracking SPTEs. We use bit 62 instead of bit 63 to avoid conflicting
- * with the SVE bit in EPT PTEs.
- */
-#define SPTE_SPECIAL_MASK (1ULL << 62)
-
 /* apic attention bits */
 #define KVM_APIC_CHECK_VAPIC	0
 /*

arch/x86/kvm/mmu.c

@@ -83,7 +83,16 @@ module_param(dbg, bool, 0644);
 #define PTE_PREFETCH_NUM		8
 
 #define PT_FIRST_AVAIL_BITS_SHIFT 10
-#define PT64_SECOND_AVAIL_BITS_SHIFT 52
+#define PT64_SECOND_AVAIL_BITS_SHIFT 54
+
+/*
+ * The mask used to denote special SPTEs, which can be either MMIO SPTEs or
+ * Access Tracking SPTEs.
+ */
+#define SPTE_SPECIAL_MASK (3ULL << 52)
+#define SPTE_AD_ENABLED_MASK (0ULL << 52)
+#define SPTE_AD_DISABLED_MASK (1ULL << 52)
+#define SPTE_MMIO_MASK (3ULL << 52)
 
 #define PT64_LEVEL_BITS 9
 
@@ -219,12 +228,11 @@ static u64 __read_mostly shadow_present_mask;
 static u64 __read_mostly shadow_me_mask;
 
 /*
- * SPTEs used by MMUs without A/D bits are marked with shadow_acc_track_value.
- * Non-present SPTEs with shadow_acc_track_value set are in place for access
- * tracking.
+ * SPTEs used by MMUs without A/D bits are marked with SPTE_AD_DISABLED_MASK;
+ * shadow_acc_track_mask is the set of bits to be cleared in non-accessed
+ * pages.
  */
 static u64 __read_mostly shadow_acc_track_mask;
-static const u64 shadow_acc_track_value = SPTE_SPECIAL_MASK;
 
 /*
  * The mask/shift to use for saving the original R/X bits when marking the PTE
@@ -304,7 +312,7 @@ void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask, u64 mmio_value, u64 access_mask)
 {
 	BUG_ON((u64)(unsigned)access_mask != access_mask);
 	BUG_ON((mmio_mask & mmio_value) != mmio_value);
-	shadow_mmio_value = mmio_value | SPTE_SPECIAL_MASK;
+	shadow_mmio_value = mmio_value | SPTE_MMIO_MASK;
 	shadow_mmio_mask = mmio_mask | SPTE_SPECIAL_MASK;
 	shadow_mmio_access_mask = access_mask;
 }
@@ -323,7 +331,7 @@ static inline bool sp_ad_disabled(struct kvm_mmu_page *sp)
 static inline bool spte_ad_enabled(u64 spte)
 {
 	MMU_WARN_ON(is_mmio_spte(spte));
-	return !(spte & shadow_acc_track_value);
+	return (spte & SPTE_SPECIAL_MASK) == SPTE_AD_ENABLED_MASK;
 }
 
 static inline u64 spte_shadow_accessed_mask(u64 spte)
@@ -461,7 +469,7 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
 {
 	BUG_ON(!dirty_mask != !accessed_mask);
 	BUG_ON(!accessed_mask && !acc_track_mask);
-	BUG_ON(acc_track_mask & shadow_acc_track_value);
+	BUG_ON(acc_track_mask & SPTE_SPECIAL_MASK);
 
 	shadow_user_mask = user_mask;
 	shadow_accessed_mask = accessed_mask;
@@ -2622,7 +2630,7 @@ static void link_shadow_page(struct kvm_vcpu *vcpu, u64 *sptep,
 	       shadow_user_mask | shadow_x_mask | shadow_me_mask;
 
 	if (sp_ad_disabled(sp))
-		spte |= shadow_acc_track_value;
+		spte |= SPTE_AD_DISABLED_MASK;
 	else
 		spte |= shadow_accessed_mask;
 
@@ -2968,7 +2976,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 
 	sp = page_header(__pa(sptep));
 	if (sp_ad_disabled(sp))
-		spte |= shadow_acc_track_value;
+		spte |= SPTE_AD_DISABLED_MASK;
 
 	/*
 	 * For the EPT case, shadow_present_mask is 0 if hardware