KVM: s390: Fix handle_{sske,pfmf} under memory pressure

KVM: s390: Fix handle_{sske,pfmf} under memory pressure

Under heavy memory pressure, handle_sske() and handle_pfmf() might
cause an endless loop if the mmu cache runs empty, the atomic
allocations fail, and the top-up function also fails. While quite
unlikely, that scenario is not impossible.

Fix the issue by not ignoring the return value of
kvm_s390_mmu_cache_topup(), and appropriately returning an error code
in case of failure.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260623153331.233784-6-imbrenda@linux.ibm.com>