Submit each reported page as a separate virtqueue buffer instead
of one buffer with an sg list of all pages. This avoids indirect
descriptor allocation (kmalloc in the reporting path) and gives
per-page used length feedback from the device.
On error, the already-queued pages are kicked and drained
before the error is returned. The caller (page_reporting_drain)
then marks the batch as unreported, which is conservative
but correct.
Note: if the virtqueue is broken, wait_event on
virtqueue_get_buf hangs. This is a pre-existing issue:
the old single-buffer code had the same hang. EVENT_IDX
is not a concern: callbacks were never disabled, so the
virtqueue manages used_event automatically.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
drivers/virtio/virtio_balloon.c | 40 +++++++++++++++++++++------------
1 file changed, 26 insertions(+), 14 deletions(-)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 6a1a610c2cb1..53b4a3984e7d 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -187,7 +187,9 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
- /* We should always be able to add one buffer to an empty queue. */
+ /* We made sure the vq is large enough so we should always
+ * be able to add one buffer to an empty queue.
+ */
virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
virtqueue_kick(vq);
@@ -202,25 +204,35 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i
struct virtio_balloon *vb =
container_of(pr_dev_info, struct virtio_balloon, pr_dev_info);
struct virtqueue *vq = vb->reporting_vq;
- unsigned int unused, err;
+ unsigned int i, err = 0;
/* We should always be able to add these buffers to an empty queue. */
- err = virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT);
+ for (i = 0; i < nents; i++) {
+ struct scatterlist one;
- /*
- * In the extremely unlikely case that something has occurred and we
- * are able to trigger an error we will simply display a warning
- * and exit without actually processing the pages.
- */
- if (WARN_ON_ONCE(err))
- return err;
+ sg_init_table(&one, 1);
+ sg_set_page(&one, sg_page(&sg[i]), sg[i].length,
+ sg[i].offset);
+ err = virtqueue_add_inbuf(vq, &one, 1, &sg[i], GFP_NOWAIT);
+ if (WARN_ON_ONCE(err)) {
+ nents = i;
+ break;
+ }
+ }
- virtqueue_kick(vq);
+ if (nents) {
+ virtqueue_kick(vq);
- /* When host has read buffer, this completes via balloon_ack */
- wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
+ /* When host has read buffer, this completes via balloon_ack */
+ for (i = 0; i < nents; i++) {
+ unsigned int unused;
- return 0;
+ wait_event(vb->acked,
+ virtqueue_get_buf(vq, &unused));
+ }
+ }
+
+ return err;
}
static void set_page_pfns(struct virtio_balloon *vb,--
MST