[PATCH net-next v2] drivers: net: xgene: Fix dma_unmap_single() size

[PATCH net-next v2] drivers: net: xgene: Fix dma_unmap_single() size

[Thomas Fourier]

In xgene_enet_refill_bufpool(), the skb->data is dma-mapped with length
len which is set to XGENE_ENET_STD_MTU which equals 1536. However, in
xgene_enet_delete_bufpool(), the same buffer is unmapped with length
XGENE_ENET_MAX_MTU which is 9600. This may erroneously unmap other
DMA buffers or cause other issues.

Change unmap length to XGENE_ENET_STD_MTU.

Fixes: a9380b0f7be8 ("drivers: net: xgene: Add support for Jumbo frame")
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
---
v1->v2:
  - Fix function name in commit description
  - Change Fixes tag

 drivers/net/ethernet/apm/xgene/xgene_enet_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
index 507db46daf2b..2ddcbf27014e 100644
--- a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
+++ b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
@@ -185,7 +185,7 @@ static void xgene_enet_delete_bufpool(struct xgene_enet_desc_ring *buf_pool)
 
 			raw_desc = &buf_pool->raw_desc16[i];
 			dma_addr = GET_VAL(DATAADDR, le64_to_cpu(raw_desc->m1));
-			dma_unmap_single(dev, dma_addr, XGENE_ENET_MAX_MTU,
+			dma_unmap_single(dev, dma_addr, XGENE_ENET_STD_MTU,
 					 DMA_FROM_DEVICE);
 		}
 	}
-- 
2.53.0

Re: [PATCH net-next v2] drivers: net: xgene: Fix dma_unmap_single() size

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - How the issue was discovered, e.g. hit in production, hit during
   development, syzbot report, manual code inspection, LLM or static
   analysis tool scan.

 - Whether the issue was actually triggered, or is only theoretical
   (e.g. found by code inspection). If it was triggered please include
   the symptoms, like the stack trace or error messages.

 - What hardware the change was tested on. For driver fixes please
   mention the device (and if relevant firmware version) used for
   testing, or say that the change was not tested on real hardware.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.

Re: [PATCH net-next v2] drivers: net: xgene: Fix dma_unmap_single() size

[Andrew Lunn]

On Thu, Oct 15, 2026 at 02:45:46PM +0200, Thomas Fourier wrote:
> In xgene_enet_refill_bufpool(), the skb->data is dma-mapped with length
> len which is set to XGENE_ENET_STD_MTU which equals 1536. However, in
> xgene_enet_delete_bufpool(), the same buffer is unmapped with length
> XGENE_ENET_MAX_MTU which is 9600. This may erroneously unmap other
> DMA buffers or cause other issues.
> 
> Change unmap length to XGENE_ENET_STD_MTU.

I don't know this driver, so i could be wrong.....

map/unmap is expensive, because it needs to flush/invalidate the cache
etc. So the hot path part of the code, dealing with real frame data,
sometimes only maps/unmaps the length of the frame, which is less than
the length of the buffer, particularly when jumbo is involved.

So you could allocate a buffer for 9600 jumbo, but in the hot path
only map/unmap part of it, but when you release the buffer, you need
to unmap the full 9600 size of the buffer, to be on the safe size.

Please look at the driver and consider this. As i said, i could be
wrong...

	Andrew

Re: [PATCH net-next v2] drivers: net: xgene: Fix dma_unmap_single() size

[Daniel Machon]

> > In xgene_enet_refill_bufpool(), the skb->data is dma-mapped with length
> > len which is set to XGENE_ENET_STD_MTU which equals 1536. However, in
> > xgene_enet_delete_bufpool(), the same buffer is unmapped with length
> > XGENE_ENET_MAX_MTU which is 9600. This may erroneously unmap other
> > DMA buffers or cause other issues.
> > 
> > Change unmap length to XGENE_ENET_STD_MTU.
> 
> I don't know this driver, so i could be wrong.....
> 
> map/unmap is expensive, because it needs to flush/invalidate the cache
> etc. So the hot path part of the code, dealing with real frame data,
> sometimes only maps/unmaps the length of the frame, which is less than
> the length of the buffer, particularly when jumbo is involved.
> 
> So you could allocate a buffer for 9600 jumbo, but in the hot path
> only map/unmap part of it, but when you release the buffer, you need
> to unmap the full 9600 size of the buffer, to be on the safe size.

I don't think that applies here. The bufpool skbs are mapped and unmapped in the
RX path with XGENE_ENET_STD_MTU, never with the frame length. The teardown unmap
with XGENE_ENET_MAX_MTU is the only mismatch (AFAICT), and that is what this
patch fixes.

> 
> Please look at the driver and consider this. As i said, i could be
> wrong...
> 
> 	Andrew
>

/Daniel

Re: [PATCH net-next v2] drivers: net: xgene: Fix dma_unmap_single() size

[Daniel Machon]

> In xgene_enet_refill_bufpool(), the skb->data is dma-mapped with length
> len which is set to XGENE_ENET_STD_MTU which equals 1536. However, in
> xgene_enet_delete_bufpool(), the same buffer is unmapped with length
> XGENE_ENET_MAX_MTU which is 9600. This may erroneously unmap other
> DMA buffers or cause other issues.
> 
> Change unmap length to XGENE_ENET_STD_MTU.

Reviewed-by: Daniel Machon <daniel.machon@microchip.com>

Re: [PATCH net-next v2] drivers: net: xgene: Fix dma_unmap_single() size

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 15 Oct 2026 14:45:46 +0200 you wrote:
> In xgene_enet_refill_bufpool(), the skb->data is dma-mapped with length
> len which is set to XGENE_ENET_STD_MTU which equals 1536. However, in
> xgene_enet_delete_bufpool(), the same buffer is unmapped with length
> XGENE_ENET_MAX_MTU which is 9600. This may erroneously unmap other
> DMA buffers or cause other issues.
> 
> Change unmap length to XGENE_ENET_STD_MTU.
> 
> [...]

Here is the summary with links:
  - [net-next,v2] drivers: net: xgene: Fix dma_unmap_single() size
    https://git.kernel.org/netdev/net-next/c/03977f8f1a63

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html