Re: [PATCH v3 1/3] net/virtio_user: convert cq descriptor IOVA address to Virtual address

[David Marchand <david.marchand@redhat.com>]

Hello Srujana, Jerin,

On Wed, Jul 3, 2024 at 12:04 PM Srujana Challa <schalla@marvell.com> wrote:
>
> This patch modifies the code to convert descriptor buffer IOVA
> addresses to virtual addresses during the processing of shadow
> control queue when IOVA mode is PA. This change enables Virtio-user
> to operate with IOVA as the descriptor buffer address.
>
> Signed-off-by: Srujana Challa <schalla@marvell.com>

This patch triggers a segfault in testpmd when using virtio-user
(server) + vhost-user (client).
This was caught in OVS unit tests running in GHA virtual machines.
In such an env with no iommu, IOVA is forced to PA.

This can be reproduced with two testpmd in an env without iommu like a
vm, or alternatively forcing --iova-mode=pa in the cmdline:

$ rm -f vhost-user; gdb ./build/app/dpdk-testpmd -ex 'run -l 0-2
--in-memory --socket-mem=512 --single-file-segments --no-pci
--file-prefix virtio
--vdev=net_virtio_user,path=vhost-user,queues=2,server=1 -- -i'
...
EAL: Selected IOVA mode 'PA'
...
vhost_user_start_server(): (vhost-user) waiting for client connection...

$ ./build/app/dpdk-testpmd -l 0,3-4 --in-memory --socket-mem=512
--single-file-segments --no-pci --file-prefix vhost-user --vdev
net_vhost,iface=vhost-user,client=1 -- -i
...
EAL: Selected IOVA mode 'PA'
...
VHOST_CONFIG: (vhost-user) virtio is now ready for processing.


On the virtio-user side:

Thread 1 "dpdk-testpmd" received signal SIGSEGV, Segmentation fault.
0x0000000002f956ab in virtio_user_handle_ctrl_msg_split
(dev=0x11a01a8d00, vring=0x11a01a8aa0, idx_hdr=0) at
../drivers/net/virtio/virtio_user/virtio_user_dev.c:942
942        if (hdr->class == VIRTIO_NET_CTRL_MQ &&
(gdb) bt
#0  0x0000000002f956ab in virtio_user_handle_ctrl_msg_split
(dev=0x11a01a8d00, vring=0x11a01a8aa0, idx_hdr=0) at
../drivers/net/virtio/virtio_user/virtio_user_dev.c:942
#1  0x0000000002f95d06 in virtio_user_handle_cq_split
(dev=0x11a01a8d00, queue_idx=4) at
../drivers/net/virtio/virtio_user/virtio_user_dev.c:1087
#2  0x0000000002f95dba in virtio_user_handle_cq (dev=0x11a01a8d00,
queue_idx=4) at
../drivers/net/virtio/virtio_user/virtio_user_dev.c:1104
#3  0x0000000002f79af7 in virtio_user_notify_queue (hw=0x11a01a8d00,
vq=0x11a0181e00) at ../drivers/net/virtio/virtio_user_ethdev.c:278
#4  0x0000000002f45408 in virtqueue_notify (vq=0x11a0181e00) at
../drivers/net/virtio/virtqueue.h:525
#5  0x0000000002f45bf0 in virtio_control_queue_notify
(vq=0x11a0181e00, cookie=0x0) at
../drivers/net/virtio/virtio_ethdev.c:227
#6  0x0000000002f404a5 in virtio_send_command_split (cvq=0x11a0181e60,
ctrl=0x7fffffffc850, dlen=0x7fffffffc84c, pkt_num=1) at
../drivers/net/virtio/virtio_cvq.c:158
#7  0x0000000002f407a7 in virtio_send_command (cvq=0x11a0181e60,
ctrl=0x7fffffffc850, dlen=0x7fffffffc84c, pkt_num=1) at
../drivers/net/virtio/virtio_cvq.c:224
#8  0x0000000002f45af7 in virtio_set_multiple_queues_auto
(dev=0x4624b80 <rte_eth_devices>, nb_queues=1) at
../drivers/net/virtio/virtio_ethdev.c:192
#9  0x0000000002f45b99 in virtio_set_multiple_queues (dev=0x4624b80
<rte_eth_devices>, nb_queues=1) at
../drivers/net/virtio/virtio_ethdev.c:210
#10 0x0000000002f4ad2d in virtio_dev_start (dev=0x4624b80
<rte_eth_devices>) at ../drivers/net/virtio/virtio_ethdev.c:2385
#11 0x0000000000aa4336 in rte_eth_dev_start (port_id=0) at
../lib/ethdev/rte_ethdev.c:1752
#12 0x00000000005984f7 in eth_dev_start_mp (port_id=0) at
../app/test-pmd/testpmd.c:642
#13 0x000000000059ddb7 in start_port (pid=65535) at
../app/test-pmd/testpmd.c:3269
#14 0x00000000005a0eea in main (argc=2, argv=0x7fffffffdfe0) at
../app/test-pmd/testpmd.c:4644
(gdb) l
937        /* locate desc for status */
938        idx_status = i;
939        n_descs++;
940
941        hdr = virtio_user_iova2virt(vring->desc[idx_hdr].addr);
942        if (hdr->class == VIRTIO_NET_CTRL_MQ &&
943            hdr->cmd == VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET) {
944            uint16_t queues, *addr;
945
946            addr = virtio_user_iova2virt(vring->desc[idx_data].addr);
(gdb) p hdr
$1 = (struct virtio_net_ctrl_hdr *) 0x0


We need someone from Marvell to fix this issue.
The next option is to revert the whole series (which was discussed and
agreed before Maxime went off, in the event this series would trigger
any issue).

-- 
David Marchand