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KVM: s390: vsie: Avoid potential deadlock with real spaces

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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: a2c17f9270 ("KVM: s390: New gmap code")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
This commit is contained in:
Claudio Imbrenda
2026-07-02 17:23:59 +02:00
committed by Christian Borntraeger
parent 7b69729046
commit 866d03de6d
1 changed files with 6 additions and 1 deletions
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7
arch/s390/kvm/gmap.c
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@@ -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;
}
}