Re: [PATCH net v5 3/3] net/smc: carry oversized SMC-Rv2 LLC messages in the queue entry

[Simon Horman]

On Sat, Aug 01, 2026 at 06:42:08PM +0900, Yehyeong Lee wrote:
> An LLC message longer than the 44-byte union smc_llc_msg arrives either
> whole in the receive buffer or split into the link group's shared v2
> buffer, and both consumers of the tail rebuild that layout themselves.
> Copy the tail into the queue entry instead, so its length and its lifetime
> are those of the message that arrived, and declare the rkeys that do fit
> inline as a member of the union rather than reaching them through a cast of
> a shorter type.
> 
> The bound the previous patch placed on links without a shared v2 receive
> buffer is no longer needed here: the extension is read from the qentry,
> whose length is the length of the message that arrived.
> 
> A DELETE_RKEY_V2 is now bounded by what arrived rather than by the buffer
> it landed in: a 44-byte message declaring 255 rkeys processed 255 of them
> before, and processes the 9 that fit now.
> 
> Suggested-by: D. Wythe <alibuda@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Yehyeong Lee <yhlee@xxxxxxxxxxxxxxxxxx>
> ---
> Measured over rxe with KASAN: a DELETE_RKEY_V2 carrying 12 rkeys over a link
> with a shared v2 receive buffer round-trips all 12 values, the last three
> coming from the copied tail; 8, 9 and 10 rkeys and a 44-byte message declaring
> 10 give 8, 9, 10 and 9 processed rkeys respectively.  kmemleak reports nothing
> over the link-addition path, and does report the queue entry when the free
> added by patch 1 is removed again.

There is an AI generated review of this patch-set available at
https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260801094208.1937951-1-yhlee%40isslab.korea.ac.kr

Of that review, I think the following warrants particular consideration.

TL;DR: to ensure complete backports, maybe add this tag to this patch,
as it has been added to patch 2/3.

  Fixes: 27ef6a9981fe ("net/smc: support SMC-R V2 for rdma devices with max_recv_sge equals to 1")

The text of the AI-generated review:

  Should this patch carry a Fixes: tag and Cc: stable as well?  Both
  predecessors in the series do, and this is the patch that changes behaviour
  in two places.

  First, the early return this hunk replaces:

	if (!smc_link_shared_v2_rxbuf(link))
		return;
  On a device with max_recv_sge == 1 that means the peer's rkeys in the
  ADD_LINK v2 extension are never installed into lgr->rtokens for the new
  link, even though those bytes do arrive on the link.  Only the
  qentry->body_len bound added here reaches them.

  Second, in smc_llc_rmt_delete_rkey() the shared-v2 path was bounded by the
  capacity of the per-lgr buffer rather than by what the peer sent:

	llcv2 = (struct smc_llc_msg_delete_rkey_v2 *)lgr->wr_rx_buf_v2;
	buf_len = SMC_WR_BUF_V2_SIZE;
	...
	max = min_t(u32, max, (buf_len - rkey_off) / sizeof(llcv2->rkey[0]));

  So a 44-byte DELETE_RKEY_V2 declaring num_rkeys = 255 walks rkey[9..254] out
  of whatever an earlier oversized peer message left in lgr->wr_rx_buf_v2 and
  passes each value to smc_rtoken_delete(), which can clear a valid rtoken of
  an unrelated connection in the same link group.

  The changelog describes both as consequences rather than as fixes:

	The bound the previous patch placed on links without a shared v2
	receive buffer is no longer needed here
	A DELETE_RKEY_V2 is now bounded by what arrived rather than by the
	buffer it landed in: a 44-byte message declaring 255 rkeys processed
	255 of them before, and processes the 9 that fit now.

  If a stable tree takes the first two patches of the series but not this one,
  does it end up with the ADD_LINK v2 extension ignored on max_recv_sge == 1
  devices and the stale-rkey deletion still present?