linux-kernel - [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: <20250516123946.1648026-2-david@redhat.com>
Date: Fri, 16 May 2025 14:39:44 +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,
	David Hildenbrand <david@...hat.com>,
	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: [PATCH v1 1/3] 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: d8dfda5af0be ("KVM: s390: pv: fix race when making a page secure")
Cc: stable@...r.kernel.org
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 arch/s390/kernel/uv.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 9a5d5be8acf41..2cc3b599c7fe3 100644
--- a/arch/s390/kernel/uv.c
+++ b/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;
-- 
2.49.0