2024-02-29 10:43:30

by Paolo Abeni

Subject: Re: [PATCH net-next v2 1/3] xsk: Remove non-zero 'dma_page' check in xp_assign_dev

On Wed, 2024-02-28 at 19:05 +0800, Yunjian Wang wrote:
> Now dma mappings are used by the physical NICs. However the vNIC
> maybe do not need them. So remove non-zero 'dma_page' check in
> xp_assign_dev.
>
> Signed-off-by: Yunjian Wang <[email protected]>
> ---
> net/xdp/xsk_buff_pool.c | 7 -------
> 1 file changed, 7 deletions(-)
>
> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index ce60ecd48a4d..a5af75b1f43c 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -219,16 +219,9 @@ int xp_assign_dev(struct xsk_buff_pool *pool,
> if (err)
> goto err_unreg_pool;
>
> - if (!pool->dma_pages) {
> - WARN(1, "Driver did not DMA map zero-copy buffers");
> - err = -EINVAL;
> - goto err_unreg_xsk;
> - }

This would unconditionally remove an otherwise valid check for most
NIC. What about let the driver declare it wont need DMA map with a
(pool?) flag.

Cheers,

Paolo

2024-02-29 13:01:19

by wangyunjian

Subject: RE: [PATCH net-next v2 1/3] xsk: Remove non-zero 'dma_page' check in xp_assign_dev

> -----Original Message-----
> From: Paolo Abeni [mailto:[email protected]]
> Sent: Thursday, February 29, 2024 6:43 PM
> To: wangyunjian <[email protected]>; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]
> Cc: [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; xudingke <[email protected]>; liwei (DT)
> <[email protected]>
> Subject: Re: [PATCH net-next v2 1/3] xsk: Remove non-zero 'dma_page' check in
> xp_assign_dev
>
> On Wed, 2024-02-28 at 19:05 +0800, Yunjian Wang wrote:
> > Now dma mappings are used by the physical NICs. However the vNIC maybe
> > do not need them. So remove non-zero 'dma_page' check in
> > xp_assign_dev.
> >
> > Signed-off-by: Yunjian Wang <[email protected]>
> > ---
> > net/xdp/xsk_buff_pool.c | 7 -------
> > 1 file changed, 7 deletions(-)
> >
> > diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c index
> > ce60ecd48a4d..a5af75b1f43c 100644
> > --- a/net/xdp/xsk_buff_pool.c
> > +++ b/net/xdp/xsk_buff_pool.c
> > @@ -219,16 +219,9 @@ int xp_assign_dev(struct xsk_buff_pool *pool,
> > if (err)
> > goto err_unreg_pool;
> >
> > - if (!pool->dma_pages) {
> > - WARN(1, "Driver did not DMA map zero-copy buffers");
> > - err = -EINVAL;
> > - goto err_unreg_xsk;
> > - }
>
> This would unconditionally remove an otherwise valid check for most NIC. What
> about let the driver declare it wont need DMA map with a
> (pool?) flag.

This check is redundant. The NIC's driver determines whether a DMA map is required.
If the NIC'driver requires the DMA map, it uses the xsk_pool_dma_map function, which
initializes the DMA map and performs a check.

Thanks

>
> Cheers,
>
> Paolo

2024-03-04 14:02:03

by Magnus Karlsson

Subject: Re: [PATCH net-next v2 1/3] xsk: Remove non-zero 'dma_page' check in xp_assign_dev

On Thu, 29 Feb 2024 at 13:52, wangyunjian <[email protected]> wrote:
>
> > -----Original Message-----
> > From: Paolo Abeni [mailto:[email protected]]
> > Sent: Thursday, February 29, 2024 6:43 PM
> > To: wangyunjian <[email protected]>; [email protected];
> > [email protected]; [email protected]; [email protected];
> > [email protected]; [email protected]; [email protected];
> > [email protected]; [email protected]
> > Cc: [email protected]; [email protected];
> > [email protected]; [email protected];
> > [email protected]; xudingke <[email protected]>; liwei (DT)
> > <[email protected]>
> > Subject: Re: [PATCH net-next v2 1/3] xsk: Remove non-zero 'dma_page' check in
> > xp_assign_dev
> >
> > On Wed, 2024-02-28 at 19:05 +0800, Yunjian Wang wrote:
> > > Now dma mappings are used by the physical NICs. However the vNIC maybe
> > > do not need them. So remove non-zero 'dma_page' check in
> > > xp_assign_dev.
> > >
> > > Signed-off-by: Yunjian Wang <[email protected]>
> > > ---
> > > net/xdp/xsk_buff_pool.c | 7 -------
> > > 1 file changed, 7 deletions(-)
> > >
> > > diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c index
> > > ce60ecd48a4d..a5af75b1f43c 100644
> > > --- a/net/xdp/xsk_buff_pool.c
> > > +++ b/net/xdp/xsk_buff_pool.c
> > > @@ -219,16 +219,9 @@ int xp_assign_dev(struct xsk_buff_pool *pool,
> > > if (err)
> > > goto err_unreg_pool;
> > >
> > > - if (!pool->dma_pages) {
> > > - WARN(1, "Driver did not DMA map zero-copy buffers");
> > > - err = -EINVAL;
> > > - goto err_unreg_xsk;
> > > - }
> >
> > This would unconditionally remove an otherwise valid check for most NIC. What
> > about let the driver declare it wont need DMA map with a
> > (pool?) flag.
>
> This check is redundant. The NIC's driver determines whether a DMA map is required.
> If the NIC'driver requires the DMA map, it uses the xsk_pool_dma_map function, which
> initializes the DMA map and performs a check.

Just to provide some context: I put this check there many years ago to
guard against a zero-copy driver writer forgetting to call
xsk_pool_dma_map() during the implementation phase. A working driver
will always have pool->dma_pages != NULL. If you both think that this
check is too much of a precaution, then I have no problem getting rid
of it. Just thought that a text warning would be nicer than a crash
later.

Thanks: Magnus

> Thanks
>
> >
> > Cheers,
> >
> > Paolo
>