s390/uv: Don't return 0 from make_hva_secure() if the operation was not successful

JIRA: https://issues.redhat.com/browse/RHEL-58218

commit 3ec8a83
Author: David Hildenbrand <david@redhat.com>
Date:   Fri May 16 14:39:44 2025 +0200

    s390/uv: Don't return 0 from make_hva_secure() if the operation was not successful

    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?

    We'll cleanup s390_wiggle_split_folio() a bit next, to also return 0
    if no split was required.

    Fixes: d8dfda5 ("KVM: s390: pv: fix race when making a page secure")
    Cc: stable@vger.kernel.org
    Signed-off-by: David Hildenbrand <david@redhat.com>
    Link: https://lore.kernel.org/r/20250516123946.1648026-2-david@redhat.com
    Message-ID: <20250516123946.1648026-2-david@redhat.com>
    Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
    Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

Signed-off-by: Thomas Huth <thuth@redhat.com>

Author: huth

arch/s390/kernel/uv.c

@@ -393,8 +393,11 @@ int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header
 	folio_walk_end(&fw, vma);
 	mmap_read_unlock(mm);
 
-	if (rc == -E2BIG || rc == -EBUSY)
+	if (rc == -E2BIG || rc == -EBUSY) {
 		rc = s390_wiggle_split_folio(mm, folio, rc == -E2BIG);
+		if (!rc)
+			rc = -EAGAIN;
+	}
 	folio_put(folio);
 
 	return rc;