[PATCH 2/2] KVM: arm64: Only update XN attr when requested during S2 relaxation

[Oliver Upton <oupton@kernel.org>]

On systems without DIC, KVM lazily grants execute permission to stage-2
translations after taking an instruction abort due to a permission
fault, allowing it to defer I-cache invalidations to the point they're
absolutely required.

If a data abort happens later down the line to such a translation, KVM
will not request execute permissions as part of the S2 relaxation on the
assumption that kvm_pgtable_stage2_relax_perms() does exactly what the
name implies and adds the requested permissions to the pre-existing
ones.

Avoid taking unintended execute permission faults by only preparing the
XN attribute if KVM_PGTABLE_PROT_X is set.

Fixes: 2608563b466b ("KVM: arm64: Add support for FEAT_XNX stage-2 permissions")
Signed-off-by: Oliver Upton <oupton@kernel.org>
---
 arch/arm64/kvm/hyp/pgtable.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 31aaca35693a..0b6d32d03efe 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1370,12 +1370,14 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
 	if (prot & KVM_PGTABLE_PROT_W)
 		set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
 
-	ret = stage2_set_xn_attr(prot, &xn);
-	if (ret)
-		return ret;
+	if (prot & KVM_PGTABLE_PROT_X) {
+		ret = stage2_set_xn_attr(prot, &xn);
+		if (ret)
+			return ret;
 
-	set |= xn & KVM_PTE_LEAF_ATTR_HI_S2_XN;
-	clr |= ~xn & KVM_PTE_LEAF_ATTR_HI_S2_XN;
+		set |= xn & KVM_PTE_LEAF_ATTR_HI_S2_XN;
+		clr |= ~xn & KVM_PTE_LEAF_ATTR_HI_S2_XN;
+	}
 
 	ret = stage2_update_leaf_attrs(pgt, addr, 1, set, clr, NULL, &level, flags);
 	if (!ret || ret == -EAGAIN)
-- 
2.47.3