[PATCH 15/20] KVM: arm64: Add support for relaxing stage-2 perms in generic page-table code

[Will Deacon]

Add support for relaxing the permissions of a stage-2 mapping (i.e.
adding additional permissions) to the generic page-table code.

Cc: Marc Zyngier <maz at kernel.org>
Cc: Quentin Perret <qperret at google.com>
Signed-off-by: Will Deacon <will at kernel.org>
---
 arch/arm64/include/asm/kvm_pgtable.h | 17 +++++++++++++++++
 arch/arm64/kvm/pgtable.c             | 20 ++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index e4d99556a22f..36f0e9e88acd 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -198,6 +198,23 @@ kvm_pte_t kvm_pgtable_stage2_mkyoung(void *cookie, u64 addr);
  */
 kvm_pte_t kvm_pgtable_stage2_mkold(void *cookie, u64 addr);
 
+/**
+ * kvm_pgtable_stage2_relax_perms() - Relax the permissions enforced by a
+ *				      page-table entry.
+ * @cookie:	Opaque cookie allocated by kvm_pgtable_stage2_alloc_cookie().
+ * @addr:	Intermediate physical address to identify the page-table entry.
+ * @prot:	Additional permissions to grant for the mapping.
+ *
+ * If there is a valid, leaf page-table entry used to translate @addr, then
+ * relax the permissions in that entry according to the read, write and
+ * execute permissions specified by @prot. No permissions are removed, and
+ * TLB invalidation is performed after updating the entry.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int kvm_pgtable_stage2_relax_perms(void *cookie, u64 addr,
+				   enum kvm_pgtable_prot prot);
+
 /**
  * kvm_pgtable_stage2_is_young() - Test whether a page-table entry has the
  *				   access flag set.
diff --git a/arch/arm64/kvm/pgtable.c b/arch/arm64/kvm/pgtable.c
index eb41f162a36a..14d8a1b2c4c1 100644
--- a/arch/arm64/kvm/pgtable.c
+++ b/arch/arm64/kvm/pgtable.c
@@ -800,6 +800,26 @@ bool kvm_pgtable_stage2_is_young(void *cookie, u64 addr)
 	return !!(pte & KVM_PTE_LEAF_ATTR_LO_S2_AF);
 }
 
+int kvm_pgtable_stage2_relax_perms(void *cookie, u64 addr,
+				   enum kvm_pgtable_prot prot)
+{
+	int ret;
+	struct kvm_pgtable *pgt = cookie;
+	kvm_pte_t set = 0, clr = 0;
+
+	if (prot & KVM_PGTABLE_PROT_R)
+		set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
+
+	if (prot & KVM_PGTABLE_PROT_W)
+		set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
+
+	if (prot & KVM_PGTABLE_PROT_X)
+		clr |= KVM_PTE_LEAF_ATTR_HI_S2_XN;
+
+	ret = stage2_update_leaf_attrs(cookie, addr, 1, set, clr, NULL);
+	kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, pgt->mmu, addr, 0);
+	return ret;
+}
 
 static int stage2_flush_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
 			       enum kvm_pgtable_walk_flags flag,
-- 
2.28.0.rc0.142.g3c755180ce-goog