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From:   Laurent Vivier <lvivier@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     Alexander Potapenko <glider@google.com>,
        linux-crypto@vger.kernel.org, Dmitriy Vyukov <dvyukov@google.com>,
        rusty@rustcorp.com.au, amit@kernel.org, akong@redhat.com,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "Michael S . Tsirkin" <mst@redhat.com>,
        Matt Mackall <mpm@selenic.com>,
        virtualization@lists.linux-foundation.org,
        Laurent Vivier <lvivier@redhat.com>
Subject: [PATCH 4/4] hwrng: virtio - always add a pending request
Date:   Wed, 22 Sep 2021 19:09:03 +0200
Message-Id: <20210922170903.577801-5-lvivier@redhat.com>
In-Reply-To: <20210922170903.577801-1-lvivier@redhat.com>
References: <20210922170903.577801-1-lvivier@redhat.com>
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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@redhat.com>
---
 drivers/char/hw_random/virtio-rng.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 8ba97cf4ca8f..0b3c9b643495 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 +43,16 @@ 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);
+
 	sg_init_one(&sg, vi->data, sizeof(vi->data));
 
 	/* There should always be room for one buffer. */
@@ -69,6 +68,8 @@ 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 +99,7 @@ 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 +121,7 @@ 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 +157,9 @@ 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 +178,6 @@ 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);
-- 
2.31.1