A virtio-vsock peer that does not consume what it is sent can make the
local side queue memory that no limit covers. On a host the peer is a
guest, and the memory is GFP_KERNEL, charged to no memory cgroup. Two
ways remain on net/main:
- the send credit trusts the fwd_cnt the peer reports, so a peer that
never reads but keeps acknowledging gets unlimited credit (patch 2);
- credit updates are not bounded at all: a peer can solicit them with
OP_CREDIT_REQUEST, or by sending small packets that a reader drains,
while posting no rx buffers (patch 3).
Patch 1 fixes the accounting of packets that vhost drops on rx errors;
patch 2 relies on bytes_unsent being right.
Nothing changes on the wire.
Tested in an x86_64 qemu/KVM guest running the kernel under test
(net/main 03897066069f); the "guest" is a user-space program driving
/dev/vhost-vsock directly, talking to plain AF_VSOCK host sockets:
case net/main this series
lying fwd_cnt, no rx buffers, 2 s of 256 MiB 256 KiB
non-blocking send() on one socket queued (one window)
20000 OP_CREDIT_REQUEST, no rx buffers +18.5 MiB +0
20000 1-byte packets, each read by host +18.0 MiB +24 KiB
vsock_test from tools/testing/vsock passes over loopback and between a
nested guest and its host. A bidirectional stress test (up to 512
connections streaming both ways, readers draining in small reads) runs
without stalls, and vsock_perf throughput stays within run-to-run noise.
With KASAN and lockdep enabled, these tests show no reports.
The reproducer (a small user-space program that drives /dev/vhost-vsock
as the guest) is available on request.
The patches, the test setup and these changelogs were prepared with an
AI coding assistant (Claude); the tests above were run as described.
Oleg Drokin (3):
vhost/vsock: release the accounting of packets dropped on rx errors
vsock/virtio: bound the send credit by bytes not yet consumed by the
transport
vsock/virtio: queue at most one credit update per socket
drivers/vhost/vsock.c | 25 +++++++--
include/linux/virtio_vsock.h | 5 ++
net/vmw_vsock/virtio_transport.c | 2 +
net/vmw_vsock/virtio_transport_common.c | 69 +++++++++++++++++++++++--
net/vmw_vsock/vsock_loopback.c | 1 +
5 files changed, 95 insertions(+), 7 deletions(-)
--
2.56.0
