Re: [PATCH v1 1/3] s390/uv: don't return 0 from make_hva_secure() if the operation was not successful

[David Hildenbrand]

On 16.05.25 14:39, David Hildenbrand wrote:
> If s390_wiggle_split_folio() returns 0 because splitting a large folio
> succeeded, we will return 0 from make_hva_secure() even though a retry
> is required. Return -EAGAIN in that case.
>
> Otherwise, we'll return 0 from gmap_make_secure(), and consequently from
> unpack_one(). In kvm_s390_pv_unpack(), we assume that unpacking
> succeeded and skip unpacking this page. Later on, we run into issues
> and fail booting the VM.
>
> So far, this issue was only observed with follow-up patches where we
> split large pagecache XFS folios. Maybe it can also be triggered with
> shmem?

Yes! I can reproduce it when allocating pages outside of the qemu process.

$ echo force > /sys/kernel/mm/transparent_hugepage/shmem_enabled
$ rm /dev/shm/vm-ram
$ fallocate -l 4G /dev/shm/vm-ram
$ /usr/libexec/qemu-kvm ... -object 
memory-backend-file,id=mem0,size=4g,share=on,mem-path=/dev/shm/vm-ram -M 
memory-backend=mem0

LOADPARM=[        ]

Using virtio-blk.
Using SCSI scheme.
.........................................................................................................................
qemu-kvm: KVM PV command 4 (KVM_PV_VERIFY) failed: header rc 102 rrc 1a 
IOCTL rc: -22
Protected boot has failed: 0xa02
Guest crashed on cpu 0: disabled-wait
PSW: 0x0002000080000000 0x0000000000004608


--
Cheers,

David / dhildenb