[PATCH v2 1/5] virtio_net: Revert "virtio_net: set the default max ring size by find_vqs()"

From: Michael S. Tsirkin
Date: Mon Aug 15 2022 - 22:01:59 EST


This reverts commit 762faee5a2678559d3dc09d95f8f2c54cd0466a7.

This has been reported to trip up guests on GCP (Google Cloud).
The reason is that virtio_find_vqs_ctx_size is broken on legacy
devices. We can in theory fix virtio_find_vqs_ctx_size but
in fact the patch itself has several other issues:

- It treats unknown speed as < 10G
- It leaves userspace no way to find out the ring size set by hypervisor
- It tests speed when link is down
- It ignores the virtio spec advice:
Both \field{speed} and \field{duplex} can change, thus the driver
is expected to re-read these values after receiving a
configuration change notification.
- It is not clear the performance impact has been tested properly

Revert the patch for now.

Reported-by: Andres Freund <andres@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220814212610.GA3690074%40roeck-us.net
Link: https://lore.kernel.org/r/20220815070203.plwjx7b3cyugpdt7%40awork3.anarazel.de
Link: https://lore.kernel.org/r/3df6bb82-1951-455d-a768-e9e1513eb667%40www.fastmail.com
Link: https://lore.kernel.org/r/FCDC5DDE-3CDD-4B8A-916F-CA7D87B547CE%40anarazel.de
Fixes: 762faee5a267 ("virtio_net: set the default max ring size by find_vqs()")
Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Tested-by: Andres Freund <andres@xxxxxxxxxxx>
Tested-by: From: Guenter Roeck <linux@xxxxxxxxxxxx>
---
drivers/net/virtio_net.c | 42 ++++------------------------------------
1 file changed, 4 insertions(+), 38 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d934774e9733..ece00b84e3a7 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3432,29 +3432,6 @@ static unsigned int mergeable_min_buf_len(struct virtnet_info *vi, struct virtqu
(unsigned int)GOOD_PACKET_LEN);
}

-static void virtnet_config_sizes(struct virtnet_info *vi, u32 *sizes)
-{
- u32 i, rx_size, tx_size;
-
- if (vi->speed == SPEED_UNKNOWN || vi->speed < SPEED_10000) {
- rx_size = 1024;
- tx_size = 1024;
-
- } else if (vi->speed < SPEED_40000) {
- rx_size = 1024 * 4;
- tx_size = 1024 * 4;
-
- } else {
- rx_size = 1024 * 8;
- tx_size = 1024 * 8;
- }
-
- for (i = 0; i < vi->max_queue_pairs; i++) {
- sizes[rxq2vq(i)] = rx_size;
- sizes[txq2vq(i)] = tx_size;
- }
-}
-
static int virtnet_find_vqs(struct virtnet_info *vi)
{
vq_callback_t **callbacks;
@@ -3462,7 +3439,6 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
int ret = -ENOMEM;
int i, total_vqs;
const char **names;
- u32 *sizes;
bool *ctx;

/* We expect 1 RX virtqueue followed by 1 TX virtqueue, followed by
@@ -3490,15 +3466,10 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
ctx = NULL;
}

- sizes = kmalloc_array(total_vqs, sizeof(*sizes), GFP_KERNEL);
- if (!sizes)
- goto err_sizes;
-
/* Parameters for control virtqueue, if any */
if (vi->has_cvq) {
callbacks[total_vqs - 1] = NULL;
names[total_vqs - 1] = "control";
- sizes[total_vqs - 1] = 64;
}

/* Allocate/initialize parameters for send/receive virtqueues */
@@ -3513,10 +3484,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
ctx[rxq2vq(i)] = true;
}

- virtnet_config_sizes(vi, sizes);
-
- ret = virtio_find_vqs_ctx_size(vi->vdev, total_vqs, vqs, callbacks,
- names, sizes, ctx, NULL);
+ ret = virtio_find_vqs_ctx(vi->vdev, total_vqs, vqs, callbacks,
+ names, ctx, NULL);
if (ret)
goto err_find;

@@ -3536,8 +3505,6 @@ static int virtnet_find_vqs(struct virtnet_info *vi)


err_find:
- kfree(sizes);
-err_sizes:
kfree(ctx);
err_ctx:
kfree(names);
@@ -3897,9 +3864,6 @@ static int virtnet_probe(struct virtio_device *vdev)
vi->curr_queue_pairs = num_online_cpus();
vi->max_queue_pairs = max_queue_pairs;

- virtnet_init_settings(dev);
- virtnet_update_settings(vi);
-
/* Allocate/initialize the rx/tx queues, and invoke find_vqs */
err = init_vqs(vi);
if (err)
@@ -3912,6 +3876,8 @@ static int virtnet_probe(struct virtio_device *vdev)
netif_set_real_num_tx_queues(dev, vi->curr_queue_pairs);
netif_set_real_num_rx_queues(dev, vi->curr_queue_pairs);

+ virtnet_init_settings(dev);
+
if (virtio_has_feature(vdev, VIRTIO_NET_F_STANDBY)) {
vi->failover = net_failover_create(vi->dev);
if (IS_ERR(vi->failover)) {
--
MST