KVM: arm64: Don't serialize if the access flag isn't set

Of course, if the PTE wasn't changed then there are absolutely no
serialization requirements. Skip the DSB for an unsuccessful update to
the access flag.

Link: https://lore.kernel.org/r/20221202185156.696189-5-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 204e59e05674d806cec28e31a4cc048f07d77a1c..aa36d896bd8c6ab6927e4c1a8dcd3a3c7ecfc4ba 100644 (file)
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1116,10 +1116,14 @@ int kvm_pgtable_stage2_wrprotect(struct kvm_pgtable *pgt, u64 addr, u64 size)
 kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr)
 {
        kvm_pte_t pte = 0;
-       stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0,
-                                &pte, NULL,
-                                KVM_PGTABLE_WALK_HANDLE_FAULT);
-       dsb(ishst);
+       int ret;
+
+       ret = stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0,
+                                      &pte, NULL,
+                                      KVM_PGTABLE_WALK_HANDLE_FAULT);
+       if (!ret)
+               dsb(ishst);
+
        return pte;
 }