[PATCH v1 1/8] KVM: s390: vsie: Avoid potential deadlock with real spaces
From: Claudio Imbrenda
Date: Thu Jul 02 2026 - 11:30:09 EST
The natural lock ordering is mmu_lock -> children_lock, but in
gmap_create_shadow() the reverse order is used when handling shadowing
of real address spaces.
Convert the inner locking of kvm->mmu_lock to a trylock; return -EAGAIN
if the lock is busy, and let the caller try again.
This path is not expected to happen in real-life scenarios, so its
performance is not important.
Fixes: a2c17f9270cc ("KVM: s390: New gmap code")
Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
---
arch/s390/kvm/gmap.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
index 298fbaecec28..8abb4f55b306 100644
--- a/arch/s390/kvm/gmap.c
+++ b/arch/s390/kvm/gmap.c
@@ -1374,8 +1374,13 @@ struct gmap *gmap_create_shadow(struct kvm_s390_mmu_cache *mc, struct gmap *pare
/* Only allow one real-space gmap shadow. */
list_for_each_entry(sg, &parent->children, list) {
if (sg->guest_asce.r) {
- scoped_guard(write_lock, &parent->kvm->mmu_lock)
+ if (write_trylock(&parent->kvm->mmu_lock)) {
gmap_unshadow(sg);
+ write_unlock(&parent->kvm->mmu_lock);
+ } else {
+ gmap_put(new);
+ return ERR_PTR(-EAGAIN);
+ }
break;
}
}
--
2.55.0