KVM: arm64: Enable retrieving protections attributes of PTEs

Introduce helper functions in the KVM stage-2 and stage-1 page-table
manipulation library allowing to retrieve the enum kvm_pgtable_prot of a
PTE. This will be useful to implement custom walkers outside of
pgtable.c.

Signed-off-by: Quentin Perret <qperret@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210809152448.1810400-17-qperret@google.com

arch/arm64/include/asm/kvm_pgtable.h

@@ -507,4 +507,24 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
  */
 int kvm_pgtable_get_leaf(struct kvm_pgtable *pgt, u64 addr,
 			 kvm_pte_t *ptep, u32 *level);
+
+/**
+ * kvm_pgtable_stage2_pte_prot() - Retrieve the protection attributes of a
+ *				   stage-2 Page-Table Entry.
+ * @pte:	Page-table entry
+ *
+ * Return: protection attributes of the page-table entry in the enum
+ *	   kvm_pgtable_prot format.
+ */
+enum kvm_pgtable_prot kvm_pgtable_stage2_pte_prot(kvm_pte_t pte);
+
+/**
+ * kvm_pgtable_hyp_pte_prot() - Retrieve the protection attributes of a stage-1
+ *				Page-Table Entry.
+ * @pte:	Page-table entry
+ *
+ * Return: protection attributes of the page-table entry in the enum
+ *	   kvm_pgtable_prot format.
+ */
+enum kvm_pgtable_prot kvm_pgtable_hyp_pte_prot(kvm_pte_t pte);
 #endif	/* __ARM64_KVM_PGTABLE_H__ */

arch/arm64/kvm/hyp/pgtable.c

@@ -363,6 +363,26 @@ static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep)
 	return 0;
 }
 
+enum kvm_pgtable_prot kvm_pgtable_hyp_pte_prot(kvm_pte_t pte)
+{
+	enum kvm_pgtable_prot prot = pte & KVM_PTE_LEAF_ATTR_HI_SW;
+	u32 ap;
+
+	if (!kvm_pte_valid(pte))
+		return prot;
+
+	if (!(pte & KVM_PTE_LEAF_ATTR_HI_S1_XN))
+		prot |= KVM_PGTABLE_PROT_X;
+
+	ap = FIELD_GET(KVM_PTE_LEAF_ATTR_LO_S1_AP, pte);
+	if (ap == KVM_PTE_LEAF_ATTR_LO_S1_AP_RO)
+		prot |= KVM_PGTABLE_PROT_R;
+	else if (ap == KVM_PTE_LEAF_ATTR_LO_S1_AP_RW)
+		prot |= KVM_PGTABLE_PROT_RW;
+
+	return prot;
+}
+
 static bool hyp_pte_needs_update(kvm_pte_t old, kvm_pte_t new)
 {
 	/*
@@ -565,6 +585,23 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p
 	return 0;
 }
 
+enum kvm_pgtable_prot kvm_pgtable_stage2_pte_prot(kvm_pte_t pte)
+{
+	enum kvm_pgtable_prot prot = pte & KVM_PTE_LEAF_ATTR_HI_SW;
+
+	if (!kvm_pte_valid(pte))
+		return prot;
+
+	if (pte & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R)
+		prot |= KVM_PGTABLE_PROT_R;
+	if (pte & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W)
+		prot |= KVM_PGTABLE_PROT_W;
+	if (!(pte & KVM_PTE_LEAF_ATTR_HI_S2_XN))
+		prot |= KVM_PGTABLE_PROT_X;
+
+	return prot;
+}
+
 static bool stage2_pte_needs_update(kvm_pte_t old, kvm_pte_t new)
 {
 	if (!kvm_pte_valid(old) || !kvm_pte_valid(new))