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

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Message-ID: <a8632cbd-704f-4ca8-b44b-fdc7e641b943@redhat.com>
Date: Fri, 16 May 2025 16:07:55 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-s390@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>, Heiko Carstens
 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
 Matthew Wilcox <willy@...radead.org>, Zi Yan <ziy@...dia.com>,
 Sebastian Mitterle <smitterl@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH v1 1/3] s390/uv: don't return 0 from make_hva_secure() if
 the operation was not successful

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