On Fri, Jul 31, 2026 at 10:10 AM <[email protected]> wrote: > From: Pravin M Bathija <[email protected]> > > The vhost-user specification (vhost-user.rst) states that no file > descriptors SHOULD be passed with VHOST_USER_REM_MEM_REG. However, > it also says: "For compatibility with existing incorrect > implementations, the back-end MAY accept messages with one file > descriptor. If a file descriptor is passed, the back-end MUST close > it without using it otherwise." > > Some front-ends, notably libblkio, reuse the same message-building > helper for both ADD_MEM_REG and REM_MEM_REG and unconditionally attach > the mapping fd. The previous implementation rejected any > REM_MEM_REG carrying a file descriptor with the error: > > expect 0 FDs for request VHOST_USER_REM_MEM_REG, received 1 > > This broke teardown and memory region hot-swap with these front-ends. > > To reproduce, run any libblkio (v1.5.0) application using the > virtio-blk-vhost-user driver against a DPDK vhost back-end. The > connection is dropped during cleanup or whenever a memory region is > unmapped and remapped. > > QEMU's libvhost-user reference back-end (vu_rem_mem_reg) already > tolerates zero or one fd in this message. Align DPDK's behavior > with both the specification's compatibility clause and the reference > implementation by accepting the message and closing any unexpected fd. > > Tested with: > - QEMU VM bring-up with runtime add/remove memory regions via > QEMU monitor > - QEMU post-copy live migration between source and destination > - SPDK vhost-blk with libblkio (fio libblkio engine, write + md5 > verify) > - libblkio alloc-mem-region and map-mem-region tests exercising > ADD_MEM_REG / REM_MEM_REG / ADD_MEM_REG cycles against SPDK > vhost-blk > > Fixes: 1d730eea6a42 ("vhost: add memory region handlers") > Cc: [email protected] > > Signed-off-by: Pravin M Bathija <[email protected]> > --- > lib/vhost/vhost_user.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c > index 020c993b29..82c62f2f64 100644 > --- a/lib/vhost/vhost_user.c > +++ b/lib/vhost/vhost_user.c > @@ -73,7 +73,7 @@ VHOST_MESSAGE_HANDLER(VHOST_USER_RESET_OWNER, > vhost_user_reset_owner, false, fal > VHOST_MESSAGE_HANDLER(VHOST_USER_SET_MEM_TABLE, vhost_user_set_mem_table, > true, true) \ > VHOST_MESSAGE_HANDLER(VHOST_USER_GET_MAX_MEM_SLOTS, > vhost_user_get_max_mem_slots, false, false) \ > VHOST_MESSAGE_HANDLER(VHOST_USER_ADD_MEM_REG, vhost_user_add_mem_reg, > true, true) \ > -VHOST_MESSAGE_HANDLER(VHOST_USER_REM_MEM_REG, vhost_user_rem_mem_reg, > false, true) \ > +VHOST_MESSAGE_HANDLER(VHOST_USER_REM_MEM_REG, vhost_user_rem_mem_reg, > true, true) \ > VHOST_MESSAGE_HANDLER(VHOST_USER_SET_LOG_BASE, vhost_user_set_log_base, > true, true) \ > VHOST_MESSAGE_HANDLER(VHOST_USER_SET_LOG_FD, vhost_user_set_log_fd, true, > true) \ > VHOST_MESSAGE_HANDLER(VHOST_USER_SET_VRING_NUM, vhost_user_set_vring_num, > false, true) \ > @@ -1811,6 +1811,13 @@ vhost_user_rem_mem_reg(struct virtio_net **pdev, > struct virtio_net *dev = *pdev; > uint32_t i; > > + /* > + * The specification says no file descriptor should be passed with > + * this message, but some front-ends send one anyway. Tolerate it > and > + * close it without using it, as the specification requires. > + */ > + close_msg_fds(ctx); > + > if (dev->mem == NULL || dev->mem->nregions == 0) { > VHOST_CONFIG_LOG(dev->ifname, ERR, "no memory regions to > remove"); > return RTE_VHOST_MSG_RESULT_ERR; > -- > 2.43.0 > > Reviewed-by: Maxime Coquelin <[email protected]>
Thanks, Maxime
