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vhost_user: fix multibuffer from linux

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Under some conditions, linux can provide several buffers
in the same element (multiple entries in the iovec array).

I didn't identify what changed between the kernel guest that
provides one buffer and the one that provides several
(doesn't seem to be a kernel change or a configuration change).

Fix the following assert:

ASSERTION FAILED in virtqueue_map_desc (virtio.c:402): num_sg < max_num_sg

What I can see is the buffer can be splitted in two iovecs:
  - vnet header
  - packet data

This change manages this special case but the real fix will be to allow
tap_add_packet() to manage iovec array.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Laurent Vivier 2025-01-15 17:22:30 +01:00 committed by Stefano Brivio
parent f04b483d15
commit 1b95bd6fa1
1 changed files with 22 additions and 6 deletions
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28
vu_common.c
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@ -18,6 +18,8 @@
#include "pcap.h"
#include "vu_common.h"
#define VU_MAX_TX_BUFFER_NB 2
/**
* vu_packet_check_range() - Check if a given memory zone is contained in
* a mapped guest memory region
@ -168,10 +170,15 @@ static void vu_handle_tx(struct vu_dev *vdev, int index,
count = 0;
out_sg_count = 0;
while (count < VIRTQUEUE_MAX_SIZE) {
while (count < VIRTQUEUE_MAX_SIZE &&
out_sg_count + VU_MAX_TX_BUFFER_NB <= VIRTQUEUE_MAX_SIZE) {
int ret;
vu_set_element(&elem[count], &out_sg[out_sg_count], NULL);
elem[count].out_num = VU_MAX_TX_BUFFER_NB;
elem[count].out_sg = &out_sg[out_sg_count];
elem[count].in_num = 0;
elem[count].in_sg = NULL;
ret = vu_queue_pop(vdev, vq, &elem[count]);
if (ret < 0)
break;
@ -181,11 +188,20 @@ static void vu_handle_tx(struct vu_dev *vdev, int index,
warn("virtio-net transmit queue contains no out buffers");
break;
}
ASSERT(elem[count].out_num == 1);
if (elem[count].out_num == 1) {
tap_add_packet(vdev->context,
elem[count].out_sg[0].iov_len - hdrlen,
(char *)elem[count].out_sg[0].iov_base +
hdrlen);
} else {
/* vnet header can be in a separate iovec */
ASSERT(elem[count].out_num == 2);
ASSERT(elem[count].out_sg[0].iov_len == (size_t)hdrlen);
tap_add_packet(vdev->context,
elem[count].out_sg[1].iov_len,
(char *)elem[count].out_sg[1].iov_base);
}
tap_add_packet(vdev->context,
elem[count].out_sg[0].iov_len - hdrlen,
(char *)elem[count].out_sg[0].iov_base + hdrlen);
count++;
}
tap_handler(vdev->context, now);