KVM: PPC: Book3S HV: radix: Do not clear partition PTE when RC or write bits do not match

Adding the write bit and RC bits to pte permissions does not require a
pte clear and flush. There should not be other bits changed here,
because restricting access or changing the PFN must have already
invalidated any existing ptes (otherwise the race is already lost).
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_64_mmu_radix.c

@@ -156,7 +156,7 @@ static void kvmppc_radix_flush_pwc(struct kvm *kvm)
 	radix__flush_pwc_lpid(kvm->arch.lpid);
 }
 
-unsigned long kvmppc_radix_update_pte(struct kvm *kvm, pte_t *ptep,
+static unsigned long kvmppc_radix_update_pte(struct kvm *kvm, pte_t *ptep,
 				      unsigned long clr, unsigned long set,
 				      unsigned long addr, unsigned int shift)
 {
@@ -360,6 +360,15 @@ static void kvmppc_unmap_free_pud_entry_table(struct kvm *kvm, pud_t *pud,
 	kvmppc_unmap_free_pmd(kvm, pmd, false);
 }
 
+/*
+ * There are a number of bits which may differ between different faults to
+ * the same partition scope entry. RC bits, in the course of cleaning and
+ * aging. And the write bit can change, either the access could have been
+ * upgraded, or a read fault could happen concurrently with a write fault
+ * that sets those bits first.
+ */
+#define PTE_BITS_MUST_MATCH (~(_PAGE_WRITE | _PAGE_DIRTY | _PAGE_ACCESSED))
+
 static int kvmppc_create_pte(struct kvm *kvm, pte_t pte, unsigned long gpa,
 			     unsigned int level, unsigned long mmu_seq)
 {
@@ -404,19 +413,28 @@ static int kvmppc_create_pte(struct kvm *kvm, pte_t pte, unsigned long gpa,
 	if (pud_huge(*pud)) {
 		unsigned long hgpa = gpa & PUD_MASK;
 
+		/* Check if we raced and someone else has set the same thing */
+		if (level == 2) {
+			if (pud_raw(*pud) == pte_raw(pte)) {
+				ret = 0;
+				goto out_unlock;
+			}
+			/* Valid 1GB page here already, add our extra bits */
+			WARN_ON_ONCE((pud_val(*pud) ^ pte_val(pte)) &
+							PTE_BITS_MUST_MATCH);
+			kvmppc_radix_update_pte(kvm, (pte_t *)pud,
+					      0, pte_val(pte), hgpa, PUD_SHIFT);
+			ret = 0;
+			goto out_unlock;
+		}
 		/*
 		 * If we raced with another CPU which has just put
 		 * a 1GB pte in after we saw a pmd page, try again.
 		 */
-		if (level <= 1 && !new_pmd) {
+		if (!new_pmd) {
 			ret = -EAGAIN;
 			goto out_unlock;
 		}
-		/* Check if we raced and someone else has set the same thing */
-		if (level == 2 && pud_raw(*pud) == pte_raw(pte)) {
-			ret = 0;
-			goto out_unlock;
-		}
 		/* Valid 1GB page here already, remove it */
 		kvmppc_unmap_pte(kvm, (pte_t *)pud, hgpa, PUD_SHIFT);
 	}
@@ -443,19 +461,29 @@ static int kvmppc_create_pte(struct kvm *kvm, pte_t pte, unsigned long gpa,
 	if (pmd_is_leaf(*pmd)) {
 		unsigned long lgpa = gpa & PMD_MASK;
 
+		/* Check if we raced and someone else has set the same thing */
+		if (level == 1) {
+			if (pmd_raw(*pmd) == pte_raw(pte)) {
+				ret = 0;
+				goto out_unlock;
+			}
+			/* Valid 2MB page here already, add our extra bits */
+			WARN_ON_ONCE((pmd_val(*pmd) ^ pte_val(pte)) &
+							PTE_BITS_MUST_MATCH);
+			kvmppc_radix_update_pte(kvm, pmdp_ptep(pmd),
+					      0, pte_val(pte), lgpa, PMD_SHIFT);
+			ret = 0;
+			goto out_unlock;
+		}
+
 		/*
 		 * If we raced with another CPU which has just put
 		 * a 2MB pte in after we saw a pte page, try again.
 		 */
-		if (level == 0 && !new_ptep) {
+		if (!new_ptep) {
 			ret = -EAGAIN;
 			goto out_unlock;
 		}
-		/* Check if we raced and someone else has set the same thing */
-		if (level == 1 && pmd_raw(*pmd) == pte_raw(pte)) {
-			ret = 0;
-			goto out_unlock;
-		}
 		/* Valid 2MB page here already, remove it */
 		kvmppc_unmap_pte(kvm, pmdp_ptep(pmd), lgpa, PMD_SHIFT);
 	}
@@ -480,19 +508,17 @@ static int kvmppc_create_pte(struct kvm *kvm, pte_t pte, unsigned long gpa,
 	}
 	ptep = pte_offset_kernel(pmd, gpa);
 	if (pte_present(*ptep)) {
-		unsigned long old;
-
 		/* Check if someone else set the same thing */
 		if (pte_raw(*ptep) == pte_raw(pte)) {
 			ret = 0;
 			goto out_unlock;
 		}
-		/* PTE was previously valid, so invalidate it */
-		old = kvmppc_radix_update_pte(kvm, ptep, _PAGE_PRESENT,
-					      0, gpa, 0);
-		kvmppc_radix_tlbie_page(kvm, gpa, 0);
-		if (old & _PAGE_DIRTY)
-			mark_page_dirty(kvm, gpa >> PAGE_SHIFT);
+		/* Valid page here already, add our extra bits */
+		WARN_ON_ONCE((pte_val(*ptep) ^ pte_val(pte)) &
+							PTE_BITS_MUST_MATCH);
+		kvmppc_radix_update_pte(kvm, ptep, 0, pte_val(pte), gpa, 0);
+		ret = 0;
+		goto out_unlock;
 	}
 	kvmppc_radix_set_pte_at(kvm, gpa, ptep, pte);
 	ret = 0;