[PATCH net] ethernet: ionic: Fix DMA mapping test in `ionic_xdp_post_frame()`

[PATCH net] ethernet: ionic: Fix DMA mapping test in `ionic_xdp_post_frame()`

[Thomas Fourier]

The `ionic_tx_map_frag()` wrapper function is used which returns 0 or a
valid DMA address.  Testing that pointer with `dma_mapping_error()`could
be eroneous since the error value exptected by `dma_mapping_error()` is
not 0 but `DMA_MAPPING_ERROR` which is often ~0.

Fixes: ac8813c0ab7d ("ionic: convert Rx queue buffers to use page_pool")
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
---
 drivers/net/ethernet/pensando/ionic/ionic_txrx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
index 2ac59564ded1..beefdc43013e 100644
--- a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
+++ b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
@@ -357,7 +357,7 @@ static int ionic_xdp_post_frame(struct ionic_queue *q, struct xdp_frame *frame,
 			} else {
 				dma_addr = ionic_tx_map_frag(q, frag, 0,
 							     skb_frag_size(frag));
-				if (dma_mapping_error(q->dev, dma_addr)) {
+				if (!dma_addr) {
 					ionic_tx_desc_unmap_bufs(q, desc_info);
 					return -EIO;
 				}
-- 
2.43.0

Re: [PATCH net] ethernet: ionic: Fix DMA mapping test in `ionic_xdp_post_frame()`

[Michal Swiatkowski]

On Tue, Jun 17, 2025 at 11:18:36AM +0200, Thomas Fourier wrote:
> The `ionic_tx_map_frag()` wrapper function is used which returns 0 or a
> valid DMA address.  Testing that pointer with `dma_mapping_error()`could
> be eroneous since the error value exptected by `dma_mapping_error()` is
> not 0 but `DMA_MAPPING_ERROR` which is often ~0.
> 
> Fixes: ac8813c0ab7d ("ionic: convert Rx queue buffers to use page_pool")
> Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
> ---
>  drivers/net/ethernet/pensando/ionic/ionic_txrx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> index 2ac59564ded1..beefdc43013e 100644
> --- a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> +++ b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> @@ -357,7 +357,7 @@ static int ionic_xdp_post_frame(struct ionic_queue *q, struct xdp_frame *frame,
>  			} else {
>  				dma_addr = ionic_tx_map_frag(q, frag, 0,
>  							     skb_frag_size(frag));
> -				if (dma_mapping_error(q->dev, dma_addr)) {
> +				if (!dma_addr) {
>  					ionic_tx_desc_unmap_bufs(q, desc_info);
>  					return -EIO;

Right, in ionic_tx_map_skb() it is used correctly (like here now).
Thanks for fixing.

Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>

>  				}
> -- 
> 2.43.0

Re: [PATCH net] ethernet: ionic: Fix DMA mapping test in `ionic_xdp_post_frame()`

[Alexander Lobakin]

From: Thomas Fourier <fourier.thomas@gmail.com>
Date: Tue, 17 Jun 2025 11:18:36 +0200

> The `ionic_tx_map_frag()` wrapper function is used which returns 0 or a
> valid DMA address.  Testing that pointer with `dma_mapping_error()`could
> be eroneous since the error value exptected by `dma_mapping_error()` is
> not 0 but `DMA_MAPPING_ERROR` which is often ~0.

BTW I remember clearly that Chris wrote that dma_addr == 0 is a
perfectly valid DMA address, that's why ~0 was picked for error checking.
So maybe it's better to fix the driver. I realize that in the real
world, it's almost impossible to get dma_addr == 0 from dma_map_*(), but
still.

> 
> Fixes: ac8813c0ab7d ("ionic: convert Rx queue buffers to use page_pool")
> Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>

Thanks,
Olek

Re: [PATCH net] ethernet: ionic: Fix DMA mapping test in `ionic_xdp_post_frame()`

[Brett Creeley]

On 6/17/2025 2:18 AM, Thomas Fourier wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
> 
> 
> The `ionic_tx_map_frag()` wrapper function is used which returns 0 or a
> valid DMA address.  Testing that pointer with `dma_mapping_error()`could
> be eroneous since the error value exptected by `dma_mapping_error()` is
> not 0 but `DMA_MAPPING_ERROR` which is often ~0.
> 
> Fixes: ac8813c0ab7d ("ionic: convert Rx queue buffers to use page_pool")
> Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
> ---
>   drivers/net/ethernet/pensando/ionic/ionic_txrx.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> index 2ac59564ded1..beefdc43013e 100644
> --- a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> +++ b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
> @@ -357,7 +357,7 @@ static int ionic_xdp_post_frame(struct ionic_queue *q, struct xdp_frame *frame,
>                          } else {
>                                  dma_addr = ionic_tx_map_frag(q, frag, 0,
>                                                               skb_frag_size(frag));
> -                               if (dma_mapping_error(q->dev, dma_addr)) {
> +                               if (!dma_addr) {

Thanks for the fix.

After looking at this and Olek's comment, I think it makes the most 
sense to return DMA_MAPPING_ERROR from ionic_tx_map_frag() and 
ionic_tx_map_single() instead of 0 on failures.

Then any callers would do the following check:

	if (unlikely(dma_addr == DMA_MAPPING_ERROR))
		/* failure path */

Another option is always returning dma_addr regardless of 
success/failure from the ionic_tx_map* functions, but then I'd be 
inclined to use dma_mapping_error() again in the caller. This approach 
seems wrong to me, especially when CONFIG_DMA_API_DEBUG is enabled.

Thanks,

Brett



>                                          ionic_tx_desc_unmap_bufs(q, desc_info);
>                                          return -EIO;
>                                  }
> --
> 2.43.0
> 

Re: [PATCH net] ethernet: ionic: Fix DMA mapping test in `ionic_xdp_post_frame()`

[Alexander Lobakin]

From: Brett Creeley <bcreeley@amd.com>
Date: Tue, 17 Jun 2025 09:56:55 -0700

> On 6/17/2025 2:18 AM, Thomas Fourier wrote:
>> Caution: This message originated from an External Source. Use proper
>> caution when opening attachments, clicking links, or responding.
>>
>>
>> The `ionic_tx_map_frag()` wrapper function is used which returns 0 or a
>> valid DMA address.  Testing that pointer with `dma_mapping_error()`could
>> be eroneous since the error value exptected by `dma_mapping_error()` is
>> not 0 but `DMA_MAPPING_ERROR` which is often ~0.
>>
>> Fixes: ac8813c0ab7d ("ionic: convert Rx queue buffers to use page_pool")
>> Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
>> ---
>>   drivers/net/ethernet/pensando/ionic/ionic_txrx.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c b/
>> drivers/net/ethernet/pensando/ionic/ionic_txrx.c
>> index 2ac59564ded1..beefdc43013e 100644
>> --- a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
>> +++ b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
>> @@ -357,7 +357,7 @@ static int ionic_xdp_post_frame(struct ionic_queue
>> *q, struct xdp_frame *frame,
>>                          } else {
>>                                  dma_addr = ionic_tx_map_frag(q, frag, 0,
>>                                                              
>> skb_frag_size(frag));
>> -                               if (dma_mapping_error(q->dev,
>> dma_addr)) {
>> +                               if (!dma_addr) {
> 
> Thanks for the fix.
> 
> After looking at this and Olek's comment, I think it makes the most
> sense to return DMA_MAPPING_ERROR from ionic_tx_map_frag() and
> ionic_tx_map_single() instead of 0 on failures.
> 
> Then any callers would do the following check:
> 
>     if (unlikely(dma_addr == DMA_MAPPING_ERROR))
>         /* failure path */
> 
> Another option is always returning dma_addr regardless of success/
> failure from the ionic_tx_map* functions, but then I'd be inclined to
> use dma_mapping_error() again in the caller. This approach seems wrong
> to me, especially when CONFIG_DMA_API_DEBUG is enabled.

Yup, I'd agree that dma_mapping_error() should be used only for checking
return values of the generic DMA API functions and only once per one
mapping. Otherwise, it's fine to pass DMA_MAPPING_ERROR and test against
it directly (after dma_mapping_error() was called already).

> 
> Thanks,
> 
> Brett

Thanks,
Olek