linux-kernel - [RFC PATCH] virtio: do not reset stateful devices on resume

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Date:   Tue, 14 Dec 2021 17:33:05 +0100
From:   Mikhail Golubev <Mikhail.Golubev@...nsynergy.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Anton Yakovlev <Anton.Yakovlev@...nsynergy.com>,
        Mikhail Golubev <Mikhail.Golubev@...nsynergy.com>
Subject: [RFC PATCH] virtio: do not reset stateful devices on resume

From: Anton Yakovlev <Anton.Yakovlev@...nsynergy.com>

We assume that stateful devices can maintain their state while
suspended. And for this reason they don't have a freeze callback. If
such a device is reset during resume, the device state/context will be
lost on the device side. And the virtual device will stop working.

Signed-off-by: Anton Yakovlev <Anton.Yakovlev@...nsynergy.com>
Signed-off-by: Mikhail Golubev <mikhail.golubev@...nsynergy.com>
---
 drivers/virtio/virtio.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 236081afe9a2..defa15b56eb8 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -472,6 +472,13 @@ int virtio_device_restore(struct virtio_device *dev)
 	struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
 	int ret;
 
+	/* Short path for stateful devices. Here we assume that if the device
+	 * does not have a freeze callback, its state was not changed when
+	 * suspended.
+	 */
+	if (drv && !drv->freeze)
+		goto on_config_enable;
+
 	/* We always start by resetting the device, in case a previous
 	 * driver messed it up. */
 	dev->config->reset(dev);
@@ -503,6 +510,7 @@ int virtio_device_restore(struct virtio_device *dev)
 	/* Finally, tell the device we're all set */
 	virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
 
+on_config_enable:
 	virtio_config_enable(dev);
 
 	return 0;
-- 
2.34.1


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