On Wed, 13 Aug 2025 04:41:09 -0400 "Michael S. Tsirkin" wrote:

On Thu, Jul 17, 2025 at 10:01:16AM +0100, Will Deacon wrote:

quoted

When transmitting a vsock packet, virtio_transport_send_pkt_info() calls
virtio_transport_alloc_linear_skb() to allocate and fill SKBs with the
transmit data. Unfortunately, these are always linear allocations and
can therefore result in significant pressure on kmalloc() considering
that the maximum packet size (VIRTIO_VSOCK_MAX_PKT_BUF_SIZE +
VIRTIO_VSOCK_SKB_HEADROOM) is a little over 64KiB, resulting in a 128KiB
allocation for each packet.

Rework the vsock SKB allocation so that, for sizes with page order
greater than PAGE_ALLOC_COSTLY_ORDER, a nonlinear SKB is allocated
instead with the packet header in the SKB and the transmit data in the
fragments. Note that this affects both the vhost and virtio transports.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>

So this caused a regression, see syzbot report:

https://lore.kernel.org/all/689a3d92.050a0220.7f033.00ff.GAE@google.com (local)

I'm inclined to revert unless we have a fix quickly.

Because recomputing skb len survived the syzbot test [1], Will looks innocent.

[1] https://lore.kernel.org/lkml/689c8d08.050a0220.7f033.014a.GAE@google.com/ (local)