Patch "hwrng: virtio - always add a pending request" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    hwrng: virtio - always add a pending request

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     hwrng-virtio-always-add-a-pending-request.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 4972e4f5d2ec4b0b026957b73f06ae148b68cd19
Author: Laurent Vivier <lvivier@xxxxxxxxxx>
Date:   Thu Oct 28 12:11:11 2021 +0200

    hwrng: virtio - always add a pending request
    
    [ Upstream commit 9a4b612d675b03f7fc9fa1957ca399c8223f3954 ]
    
    If we ensure we have already some data available by enqueuing
    again the buffer once data are exhausted, we can return what we
    have without waiting for the device answer.
    
    Signed-off-by: Laurent Vivier <lvivier@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20211028101111.128049-5-lvivier@xxxxxxxxxx
    Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Stable-dep-of: ac52578d6e8d ("hwrng: virtio - Fix race on data_avail and actual data")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 8ba97cf4ca8fb..0a7dde135db19 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -20,7 +20,6 @@ struct virtrng_info {
 	struct virtqueue *vq;
 	char name[25];
 	int index;
-	bool busy;
 	bool hwrng_register_done;
 	bool hwrng_removed;
 	/* data transfer */
@@ -44,16 +43,18 @@ static void random_recv_done(struct virtqueue *vq)
 		return;
 
 	vi->data_idx = 0;
-	vi->busy = false;
 
 	complete(&vi->have_data);
 }
 
-/* The host will fill any buffer we give it with sweet, sweet randomness. */
-static void register_buffer(struct virtrng_info *vi)
+static void request_entropy(struct virtrng_info *vi)
 {
 	struct scatterlist sg;
 
+	reinit_completion(&vi->have_data);
+	vi->data_avail = 0;
+	vi->data_idx = 0;
+
 	sg_init_one(&sg, vi->data, sizeof(vi->data));
 
 	/* There should always be room for one buffer. */
@@ -69,6 +70,8 @@ static unsigned int copy_data(struct virtrng_info *vi, void *buf,
 	memcpy(buf, vi->data + vi->data_idx, size);
 	vi->data_idx += size;
 	vi->data_avail -= size;
+	if (vi->data_avail == 0)
+		request_entropy(vi);
 	return size;
 }
 
@@ -98,13 +101,7 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
 	 * so either size is 0 or data_avail is 0
 	 */
 	while (size != 0) {
-		/* data_avail is 0 */
-		if (!vi->busy) {
-			/* no pending request, ask for more */
-			vi->busy = true;
-			reinit_completion(&vi->have_data);
-			register_buffer(vi);
-		}
+		/* data_avail is 0 but a request is pending */
 		ret = wait_for_completion_killable(&vi->have_data);
 		if (ret < 0)
 			return ret;
@@ -126,8 +123,7 @@ static void virtio_cleanup(struct hwrng *rng)
 {
 	struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
 
-	if (vi->busy)
-		complete(&vi->have_data);
+	complete(&vi->have_data);
 }
 
 static int probe_common(struct virtio_device *vdev)
@@ -163,6 +159,9 @@ static int probe_common(struct virtio_device *vdev)
 		goto err_find;
 	}
 
+	/* we always have a pending entropy request */
+	request_entropy(vi);
+
 	return 0;
 
 err_find:
@@ -181,7 +180,6 @@ static void remove_common(struct virtio_device *vdev)
 	vi->data_idx = 0;
 	complete(&vi->have_data);
 	vdev->config->reset(vdev);
-	vi->busy = false;
 	if (vi->hwrng_register_done)
 		hwrng_unregister(&vi->hwrng);
 	vdev->config->del_vqs(vdev);