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: [email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Message-ID: <[email protected]>
Reviewed-by: Claudio Imbrenda <[email protected]>
Signed-off-by: Claudio Imbrenda <[email protected]>

Author: davidhildenbrand

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;