[PATCH v2 17/28] KVM: arm64: Don't update descriptors for "non-arch" access

[Oliver Upton <oupton@kernel.org>]

WALK_ACCESS_NONARCH is a special indicator that the page table walk
request is not due to an architectural behavior and instead used
internally for KVM. Currently, the only user of this is SEA injection to
identify the correct translation level that generated the abort.

Ensure "non-arch" table walks are not made visible to the guest and
explicitly avoid descriptor updates. These accesses are not expected to
be used for pseudo-TLB fills, nor are they used to dirty any memory.

Reviewed-by: Leonardo Bras <leo.bras@arm.com>
Signed-off-by: Oliver Upton <oupton@kernel.org>
---
 arch/arm64/kvm/at.c     | 15 ++++++++++++++-
 arch/arm64/kvm/nested.c | 12 +++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
index 20cc50c0f694..2ce34af3b9f2 100644
--- a/arch/arm64/kvm/at.c
+++ b/arch/arm64/kvm/at.c
@@ -457,6 +457,15 @@ static int kvm_read_s1_desc(struct kvm_vcpu *vcpu, u64 pa, u64 *desc,
 	return 0;
 }
 
+static bool should_set_access_flag(struct s1_walk_info *wi, struct s1_walk_step *ws,
+				   struct kvm_walk_access *access)
+{
+	if (access->type == WALK_ACCESS_NONARCH)
+		return false;
+
+	return wi->ha;
+}
+
 static bool should_set_dirty_state(struct s1_walk_info *wi, struct s1_walk_step *ws,
 				   struct s1_walk_result *wr, struct kvm_walk_access *access)
 {
@@ -466,6 +475,7 @@ static bool should_set_dirty_state(struct s1_walk_info *wi, struct s1_walk_step
 	/* R_RKMHW */
 	case WALK_ACCESS_CMO:
 	case WALK_ACCESS_AT:
+	case WALK_ACCESS_NONARCH:
 		return false;
 	default:
 		/* R_NSXRD */
@@ -482,7 +492,7 @@ static int handle_desc_update(struct kvm_vcpu *vcpu, struct s1_walk_info *wi,
 
 	old = new = ws->desc;
 
-	if (wi->ha)
+	if (should_set_access_flag(wi, ws, access))
 		new |= PTE_AF;
 
 	if (should_set_dirty_state(wi, ws, wr, access))
@@ -558,6 +568,9 @@ static int walk_s1(struct kvm_vcpu *vcpu, struct s1_walk_info *wi,
 				.write	= wi->ha,
 			};
 
+			if (access->type == WALK_ACCESS_NONARCH)
+				s2_access.type = WALK_ACCESS_NONARCH;
+
 			ret = kvm_walk_nested_s2(vcpu, &s2_access, &ws.s2_trans);
 			if (ret == -EAGAIN)
 				return ret;
diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 964331dbf475..7dda95d37925 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -247,6 +247,15 @@ static int read_guest_s2_desc(struct kvm_vcpu *vcpu, struct s2_walk_step *ws,
 	return 0;
 }
 
+static bool should_set_access_flag(struct s2_walk_info *wi, struct s2_walk_step *ws,
+				   struct kvm_walk_access *access)
+{
+	if (access->type == WALK_ACCESS_NONARCH)
+		return false;
+
+	return wi->ha;
+}
+
 static bool should_set_dirty_state(struct s2_walk_info *wi, struct s2_walk_step *ws,
 				   struct kvm_s2_trans *out, struct kvm_walk_access *access)
 {
@@ -254,6 +263,7 @@ static bool should_set_dirty_state(struct s2_walk_info *wi, struct s2_walk_step
 	/* R_ZYGHJ */
 	case WALK_ACCESS_CMO:
 	case WALK_ACCESS_AT:
+	case WALK_ACCESS_NONARCH:
 		return false;
 	default:
 		/* R_NSXRD */
@@ -270,7 +280,7 @@ static int handle_desc_update(struct kvm_vcpu *vcpu, struct s2_walk_info *wi,
 
 	old = new = ws->desc;
 
-	if (wi->ha)
+	if (should_set_access_flag(wi, ws, access))
 		new |= KVM_PTE_LEAF_ATTR_LO_S2_AF;
 
 	if (should_set_dirty_state(wi, ws, out, access))
-- 
2.47.3