[PATCH v2] smb: smbdirect: fix MR registration for coalesced SG lists

[PATCH v2] smb: smbdirect: fix MR registration for coalesced SG lists

[Yi Kuo]

ib_dma_map_sg() modifies the provided scatterlist and returns the
number of mapped entries, which can be fewer than the requested
mr->sgt.nents if the DMA controller coalesces contiguous memory
segments. Passing the original, uncoalesced count to ib_map_mr_sg()
causes memory registration failures if coalescing actually occurs.

Capture the actual mapped count returned by ib_dma_map_sg() and pass it
to ib_map_mr_sg() to ensure correct MR registration.

Also update the ib_dma_map_sg() error logging to drop the error
pointer formatting, since the return value is an integer count
rather than an error code.

Ensure a proper error code (-EIO) is assigned when DMA mapping or
MR registration fails.

Fixes: de5ef8ec3c46 ("smb: smbdirect: introduce smbdirect_mr.c with client mr code")
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221408
Signed-off-by: Yi Kuo <yi@yikuo.dev>
---
v2:
- Add proper -EIO error assignment on mapping/registration failures.
- Add Fixes and Closes tags.

 fs/smb/smbdirect/mr.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/fs/smb/smbdirect/mr.c b/fs/smb/smbdirect/mr.c
index 5228e699cd5d..5a428ff1b369 100644
--- a/fs/smb/smbdirect/mr.c
+++ b/fs/smb/smbdirect/mr.c
@@ -269,7 +269,7 @@ smbdirect_connection_register_mr_io(struct smbdirect_socket *sc,
 {
 	const struct smbdirect_socket_parameters *sp = &sc->parameters;
 	struct smbdirect_mr_io *mr;
-	int ret, num_pages;
+	int ret, num_pages, num_mapped;
 	struct ib_reg_wr *reg_wr;
 
 	num_pages = iov_iter_npages(iter, sp->max_frmr_depth + 1);
@@ -300,19 +300,22 @@ smbdirect_connection_register_mr_io(struct smbdirect_socket *sc,
 		num_pages, iov_iter_count(iter), sp->max_frmr_depth);
 	smbdirect_iter_to_sgt(iter, &mr->sgt, sp->max_frmr_depth);
 
-	ret = ib_dma_map_sg(sc->ib.dev, mr->sgt.sgl, mr->sgt.nents, mr->dir);
-	if (!ret) {
+	num_mapped = ib_dma_map_sg(sc->ib.dev, mr->sgt.sgl, mr->sgt.nents, mr->dir);
+	if (!num_mapped) {
 		smbdirect_log_rdma_mr(sc, SMBDIRECT_LOG_ERR,
-			"ib_dma_map_sg num_pages=%u dir=%x ret=%d (%1pe)\n",
-			num_pages, mr->dir, ret, SMBDIRECT_DEBUG_ERR_PTR(ret));
+			"ib_dma_map_sg num_pages=%u dir=%x num_mapped=%d\n",
+			num_pages, mr->dir, num_mapped);
+		ret = -EIO;
 		goto dma_map_error;
 	}
 
-	ret = ib_map_mr_sg(mr->mr, mr->sgt.sgl, mr->sgt.nents, NULL, PAGE_SIZE);
-	if (ret != mr->sgt.nents) {
+	ret = ib_map_mr_sg(mr->mr, mr->sgt.sgl, num_mapped, NULL, PAGE_SIZE);
+	if (ret != num_mapped) {
 		smbdirect_log_rdma_mr(sc, SMBDIRECT_LOG_ERR,
-			"ib_map_mr_sg failed ret = %d nents = %u\n",
-			ret, mr->sgt.nents);
+			"ib_map_mr_sg failed ret = %d num_mapped = %u\n",
+			ret, num_mapped);
+		if (ret >= 0)
+			ret = -EIO;
 		goto map_mr_error;
 	}
 
-- 
2.54.0

Re: [PATCH v2] smb: smbdirect: fix MR registration for coalesced SG lists

[Stefan Metzmacher]

Am 29.04.26 um 12:00 schrieb Yi Kuo:
> ib_dma_map_sg() modifies the provided scatterlist and returns the
> number of mapped entries, which can be fewer than the requested
> mr->sgt.nents if the DMA controller coalesces contiguous memory
> segments. Passing the original, uncoalesced count to ib_map_mr_sg()
> causes memory registration failures if coalescing actually occurs.
> 
> Capture the actual mapped count returned by ib_dma_map_sg() and pass it
> to ib_map_mr_sg() to ensure correct MR registration.
> 
> Also update the ib_dma_map_sg() error logging to drop the error
> pointer formatting, since the return value is an integer count
> rather than an error code.
> 
> Ensure a proper error code (-EIO) is assigned when DMA mapping or
> MR registration fails.
> 
> Fixes: de5ef8ec3c46 ("smb: smbdirect: introduce smbdirect_mr.c with client mr code")
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221408
> Signed-off-by: Yi Kuo <yi@yikuo.dev>

Reviewed-by: Stefan Metzmacher <metze@samba.org>

Thanks!
metze

Re: [PATCH v2] smb: smbdirect: fix MR registration for coalesced SG lists

[Namjae Jeon]

On Wed, Apr 29, 2026 at 7:00 PM Yi Kuo <yi@yikuo.dev> wrote:
>
> ib_dma_map_sg() modifies the provided scatterlist and returns the
> number of mapped entries, which can be fewer than the requested
> mr->sgt.nents if the DMA controller coalesces contiguous memory
> segments. Passing the original, uncoalesced count to ib_map_mr_sg()
> causes memory registration failures if coalescing actually occurs.
>
> Capture the actual mapped count returned by ib_dma_map_sg() and pass it
> to ib_map_mr_sg() to ensure correct MR registration.
>
> Also update the ib_dma_map_sg() error logging to drop the error
> pointer formatting, since the return value is an integer count
> rather than an error code.
>
> Ensure a proper error code (-EIO) is assigned when DMA mapping or
> MR registration fails.
>
> Fixes: de5ef8ec3c46 ("smb: smbdirect: introduce smbdirect_mr.c with client mr code")
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221408
> Signed-off-by: Yi Kuo <yi@yikuo.dev>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Thanks!

Re: [PATCH v2] smb: smbdirect: fix MR registration for coalesced SG lists

[Steve French]

merged into ksmbd-for-next

On Wed, Apr 29, 2026 at 5:17 AM Namjae Jeon <linkinjeon@kernel.org> wrote:
>
> On Wed, Apr 29, 2026 at 7:00 PM Yi Kuo <yi@yikuo.dev> wrote:
> >
> > ib_dma_map_sg() modifies the provided scatterlist and returns the
> > number of mapped entries, which can be fewer than the requested
> > mr->sgt.nents if the DMA controller coalesces contiguous memory
> > segments. Passing the original, uncoalesced count to ib_map_mr_sg()
> > causes memory registration failures if coalescing actually occurs.
> >
> > Capture the actual mapped count returned by ib_dma_map_sg() and pass it
> > to ib_map_mr_sg() to ensure correct MR registration.
> >
> > Also update the ib_dma_map_sg() error logging to drop the error
> > pointer formatting, since the return value is an integer count
> > rather than an error code.
> >
> > Ensure a proper error code (-EIO) is assigned when DMA mapping or
> > MR registration fails.
> >
> > Fixes: de5ef8ec3c46 ("smb: smbdirect: introduce smbdirect_mr.c with client mr code")
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221408
> > Signed-off-by: Yi Kuo <yi@yikuo.dev>
> Acked-by: Namjae Jeon <linkinjeon@kernel.org>
> Thanks!



-- 
Thanks,

Steve