[PATCH 3/6] KVM: arm64: Make stage2_pte_cacheable() return false when S2_AS_S1 is set

Marc Zyngier
2026-01-19T10:56:57Z

We cannot tell from the S2 attributes whether what we map is memory
or not when S2_AS_S1 is set, and issuing a CMO on device memory may
not be the best idea.

In this particular case, pretend that the mapping isn't cacheable.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/hyp/pgtable.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 3c5f399b1b986..07561a227f75e 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -911,6 +911,14 @@ static void stage2_unmap_put_pte(const struct kvm_pgtable_visit_ctx *ctx,
static bool stage2_pte_cacheable(struct kvm_pgtable *pgt, kvm_pte_t pte)
{
u64 memattr = pte & KVM_PTE_LEAF_ATTR_LO_S2_MEMATTR;
+
+ /*
+ * With S2_AS_S1, we have no idea whether the OA is actual memory or
+ * a device. Don't even try a CMO on that.
+ */
+ if (pgt->flags & KVM_PGTABLE_S2_AS_S1)
+ return false;
+
return kvm_pte_valid(pte) && memattr == KVM_S2_MEMATTR(pgt, NORMAL);
}

--
2.47.3