linux-kernel - [PATCH] virtio_balloon: clear modern features under legacy

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Message-ID: <20200710113046.421366-1-mst@redhat.com>
Date:   Fri, 10 Jul 2020 07:31:34 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        Alexander Duyck <alexander.duyck@...il.com>
Subject: [PATCH] virtio_balloon: clear modern features under legacy

Page reporting features were never supported by legacy hypervisors.
Supporting them poses a problem: should we use native endian-ness (like
current code assumes)? Or little endian-ness like the virtio spec says?
Rather than try to figure out, and since results of
incorrect endian-ness are dire, let's just block this configuration.

Cc: stable@...r.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/virtio/virtio_balloon.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 5d4b891bf84f..b9bc03345157 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -1107,6 +1107,15 @@ static int virtballoon_restore(struct virtio_device *vdev)
 
 static int virtballoon_validate(struct virtio_device *vdev)
 {
+	/*
+	 * Legacy devices never specified how modern features should behave.
+	 * E.g. which endian-ness to use? Better not to assume anything.
+	 */
+	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT);
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
+	}
 	/*
 	 * Inform the hypervisor that our pages are poisoned or
 	 * initialized. If we cannot do that then we should disable
-- 
MST