net/smc: cap allocation order for SMC-R physically contiguous buffers

The alloc_pages() cannot satisfy requests exceeding MAX_PAGE_ORDER,
and attempting such allocations will lead to guaranteed failures
and potential kernel warnings.

For SMCR_PHYS_CONT_BUFS, cap the allocation order to MAX_PAGE_ORDER.
This ensures the attempts to allocate the largest possible physically
contiguous chunk succeed, instead of failing with an invalid order.
This also avoids redundant "try-fail-degrade" cycles in
__smc_buf_create().

For SMCR_MIXED_BUFS, no cap is needed: if the order exceeds
MAX_PAGE_ORDER, alloc_pages() will silently fail (__GFP_NOWARN)
and automatically fall back to virtual memory.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Link: https://patch.msgid.link/20260429021637.21815-1-alibuda@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index e2d083daeb7e81a73773f019256b39972a460c46..cf6b620fef05f999e90eb8247f1f6a4d3ed187c6 100644 (file)
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -2440,6 +2440,10 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
                /* use socket send buffer size (w/o overhead) as start value */
                bufsize = smc->sk.sk_sndbuf / 2;
 
+       /* limit bufsize for physically contiguous buffers */
+       if (!is_smcd && lgr->buf_type == SMCR_PHYS_CONT_BUFS)
+               bufsize = min_t(int, bufsize, PAGE_SIZE << MAX_PAGE_ORDER);
+
        for (bufsize_comp = smc_compress_bufsize(bufsize, is_smcd, is_rmb);
             bufsize_comp >= 0; bufsize_comp--) {
                if (is_rmb) {