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KVM: s390: Fix _gaccess_shadow_fault()

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In some circumstances, it is possible that the page of nested guest
memory that is being shadowed is not present at all in the parent guest
gmap. dat_entry_walk() will not find any leaf entry and return with
-ENOENT, which will erroneously be propagated all the way to userspace.

Fix by manually calling gmap_link() on the memory of the nested guest
that is being shadowed if the mapping was not already present.

Fixes: e38c884df9 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260828115439.145885-4-imbrenda@linux.ibm.com>
This commit is contained in:
Claudio Imbrenda 2026-08-28 13:54:34 +02:00
parent ae12d2f9c1
commit faff4c8ff3
1 changed files with 13 additions and 0 deletions
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13
arch/s390/kvm/s390/gaccess.c
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@ -1589,12 +1589,25 @@ static inline int ___gaccess_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *sg
parent = READ_ONCE(sg->parent);
if (!parent)
return -EAGAIN;
retry:
scoped_guard(spinlock, &parent->children_lock) {
if (READ_ONCE(sg->parent) != parent)
return -EAGAIN;
sg->invalidated = false;
rc = _gaccess_do_shadow(vcpu->arch.mc, sg, saddr, walk);
}
if (rc == -ENOENT) {
struct kvm_memory_slot *slot;
struct guest_fault *entries;
entries = get_entries(walk);
slot = kvm_vcpu_gfn_to_memslot(vcpu, entries[LEVEL_MEM].gfn);
if (!slot)
return PGM_ADDRESSING;
rc = gmap_link(vcpu->arch.mc, parent, entries + LEVEL_MEM, slot);
if (!rc)
goto retry;
}
if (!rc)
kvm_s390_release_faultin_array(vcpu->kvm, walk->raw_entries, false);
return rc;