kvm: x86: mmu: Introduce a no-tracking version of mmu_spte_update

mmu_spte_update() tracks changes in the accessed/dirty state of
the SPTE being updated and calls kvm_set_pfn_accessed/dirty
appropriately. However, in some cases (e.g. when aging the SPTE),
this shouldn't be done. mmu_spte_update_no_track() is introduced
for use in such cases.
Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -528,27 +528,19 @@ static void mmu_spte_set(u64 *sptep, u64 new_spte)
 	__set_spte(sptep, new_spte);
 }
 
-/* Rules for using mmu_spte_update:
- * Update the state bits, it means the mapped pfn is not changed.
- *
- * Whenever we overwrite a writable spte with a read-only one we
- * should flush remote TLBs. Otherwise rmap_write_protect
- * will find a read-only spte, even though the writable spte
- * might be cached on a CPU's TLB, the return value indicates this
- * case.
- *
- * Returns true if the TLB needs to be flushed
+/*
+ * Update the SPTE (excluding the PFN), but do not track changes in its
+ * accessed/dirty status.
  */
-static bool mmu_spte_update(u64 *sptep, u64 new_spte)
+static u64 mmu_spte_update_no_track(u64 *sptep, u64 new_spte)
 {
 	u64 old_spte = *sptep;
-	bool flush = false;
 
 	WARN_ON(!is_shadow_present_pte(new_spte));
 
 	if (!is_shadow_present_pte(old_spte)) {
 		mmu_spte_set(sptep, new_spte);
-		return flush;
+		return old_spte;
 	}
 
 	if (!spte_has_volatile_bits(old_spte))
@@ -558,6 +550,28 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
 
 	WARN_ON(spte_to_pfn(old_spte) != spte_to_pfn(new_spte));
 
+	return old_spte;
+}
+
+/* Rules for using mmu_spte_update:
+ * Update the state bits, it means the mapped pfn is not changed.
+ *
+ * Whenever we overwrite a writable spte with a read-only one we
+ * should flush remote TLBs. Otherwise rmap_write_protect
+ * will find a read-only spte, even though the writable spte
+ * might be cached on a CPU's TLB, the return value indicates this
+ * case.
+ *
+ * Returns true if the TLB needs to be flushed
+ */
+static bool mmu_spte_update(u64 *sptep, u64 new_spte)
+{
+	bool flush = false;
+	u64 old_spte = mmu_spte_update_no_track(sptep, new_spte);
+
+	if (!is_shadow_present_pte(old_spte))
+		return false;
+
 	/*
 	 * For the spte updated out of mmu-lock is safe, since
 	 * we always atomically update it, see the comments in