[PATCH net] net: add net_iov_init() and use it to initialize ->page_type

[PATCH net] net: add net_iov_init() and use it to initialize ->page_type

[Jakub Kicinski]

Commit db359fccf212 ("mm: introduce a new page type for page pool in
page type") added a page_type field to struct net_iov at the same
offset as struct page::page_type, so that page_pool_set_pp_info() can
call __SetPageNetpp() uniformly on both pages and net_iovs.

The page-type API requires the field to hold the UINT_MAX "no type"
sentinel before a type can be set; for real struct page that invariant
is established by the page allocator on free. struct net_iov is not
allocated through the page allocator, so the field is left as zero
(io_uring zcrx, which uses __GFP_ZERO) or as slab garbage (devmem,
which uses kvmalloc_objs() without zeroing). When the page pool then
calls page_pool_set_pp_info() on a freshly-bound niov,
__SetPageNetpp()'s VM_BUG_ON_PAGE(page->page_type != UINT_MAX) fires
and the kernel BUGs. Triggered in selftests by io_uring zcrx setup
through the fbnic queue restart path:

 kernel BUG at ./include/linux/page-flags.h:1062!
 RIP: 0010:page_pool_set_pp_info (./include/linux/page-flags.h:1062
                                  net/core/page_pool.c:716)
 Call Trace:
  <TASK>
  net_mp_niov_set_page_pool (net/core/page_pool.c:1360)
  io_pp_zc_alloc_netmems (io_uring/zcrx.c:1089 io_uring/zcrx.c:1110)
  fbnic_fill_bdq (./include/net/page_pool/helpers.h:160
                  drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:906)
  __fbnic_nv_restart (drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2470
                      drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2874)
  fbnic_queue_start (drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2903)
  netdev_rx_queue_reconfig (net/core/netdev_rx_queue.c:137)
  __netif_mp_open_rxq (net/core/netdev_rx_queue.c:234)
  io_register_zcrx (io_uring/zcrx.c:818 io_uring/zcrx.c:903)
  __io_uring_register (io_uring/register.c:931)
  __do_sys_io_uring_register (io_uring/register.c:1029)
  do_syscall_64 (arch/x86/entry/syscall_64.c:63
                 arch/x86/entry/syscall_64.c:94)
  </TASK>

The same path is reachable through devmem dmabuf binding via
netdev_nl_bind_rx_doit() -> net_devmem_bind_dmabuf_to_queue().

Add a net_iov_init() helper that stamps ->owner, ->type and the
->page_type sentinel, and use it from both the devmem and io_uring
zcrx niov init loops.

Fixes: db359fccf212 ("mm: introduce a new page type for page pool in page type")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: asml.silence@gmail.com
CC: axboe@kernel.dk
CC: almasrymina@google.com
CC: sdf@fomichev.me
CC: hawk@kernel.org
CC: akpm@linux-foundation.org
CC: rppt@kernel.org
CC: vbabka@kernel.org
CC: io-uring@vger.kernel.org
---
 include/net/netmem.h | 15 +++++++++++++++
 io_uring/zcrx.c      |  3 +--
 net/core/devmem.c    |  3 +--
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/net/netmem.h b/include/net/netmem.h
index 507b74c9f52d..78fe51e5756b 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -127,6 +127,21 @@ static inline unsigned int net_iov_idx(const struct net_iov *niov)
 	return niov - net_iov_owner(niov)->niovs;
 }
 
+/* Initialize a niov: stamp the owning area, the memory provider type,
+ * and the page_type "no type" sentinel expected by the page-type API
+ * (see PAGE_TYPE_OPS in <linux/page-flags.h>) so that
+ * page_pool_set_pp_info() can later call __SetPageNetpp() on a niov
+ * cast to struct page.
+ */
+static inline void net_iov_init(struct net_iov *niov,
+				struct net_iov_area *owner,
+				enum net_iov_type type)
+{
+	niov->owner = owner;
+	niov->type = type;
+	niov->page_type = UINT_MAX;
+}
+
 /* netmem */
 
 /**
diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index 7b93c87b8371..19837e0b5e91 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -495,10 +495,9 @@ static int io_zcrx_create_area(struct io_zcrx_ifq *ifq,
 	for (i = 0; i < nr_iovs; i++) {
 		struct net_iov *niov = &area->nia.niovs[i];
 
-		niov->owner = &area->nia;
+		net_iov_init(niov, &area->nia, NET_IOV_IOURING);
 		area->freelist[i] = i;
 		atomic_set(&area->user_refs[i], 0);
-		niov->type = NET_IOV_IOURING;
 	}
 
 	if (ifq->dev) {
diff --git a/net/core/devmem.c b/net/core/devmem.c
index cde4c89bc146..468344739db2 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -297,8 +297,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 
 		for (i = 0; i < owner->area.num_niovs; i++) {
 			niov = &owner->area.niovs[i];
-			niov->type = NET_IOV_DMABUF;
-			niov->owner = &owner->area;
+			net_iov_init(niov, &owner->area, NET_IOV_DMABUF);
 			page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov),
 						      net_devmem_get_dma_addr(niov));
 			if (direction == DMA_TO_DEVICE)
-- 
2.53.0

Re: [PATCH net] net: add net_iov_init() and use it to initialize ->page_type

[Vlastimil Babka (SUSE)]

+Cc Byungchul

On 4/28/26 04:53, Jakub Kicinski wrote:
> Commit db359fccf212 ("mm: introduce a new page type for page pool in
> page type") added a page_type field to struct net_iov at the same
> offset as struct page::page_type, so that page_pool_set_pp_info() can
> call __SetPageNetpp() uniformly on both pages and net_iovs.
> 
> The page-type API requires the field to hold the UINT_MAX "no type"
> sentinel before a type can be set; for real struct page that invariant
> is established by the page allocator on free. struct net_iov is not
> allocated through the page allocator, so the field is left as zero
> (io_uring zcrx, which uses __GFP_ZERO) or as slab garbage (devmem,
> which uses kvmalloc_objs() without zeroing). When the page pool then
> calls page_pool_set_pp_info() on a freshly-bound niov,
> __SetPageNetpp()'s VM_BUG_ON_PAGE(page->page_type != UINT_MAX) fires
> and the kernel BUGs. Triggered in selftests by io_uring zcrx setup
> through the fbnic queue restart path:
> 
>  kernel BUG at ./include/linux/page-flags.h:1062!
>  RIP: 0010:page_pool_set_pp_info (./include/linux/page-flags.h:1062
>                                   net/core/page_pool.c:716)
>  Call Trace:
>   <TASK>
>   net_mp_niov_set_page_pool (net/core/page_pool.c:1360)
>   io_pp_zc_alloc_netmems (io_uring/zcrx.c:1089 io_uring/zcrx.c:1110)
>   fbnic_fill_bdq (./include/net/page_pool/helpers.h:160
>                   drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:906)
>   __fbnic_nv_restart (drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2470
>                       drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2874)
>   fbnic_queue_start (drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2903)
>   netdev_rx_queue_reconfig (net/core/netdev_rx_queue.c:137)
>   __netif_mp_open_rxq (net/core/netdev_rx_queue.c:234)
>   io_register_zcrx (io_uring/zcrx.c:818 io_uring/zcrx.c:903)
>   __io_uring_register (io_uring/register.c:931)
>   __do_sys_io_uring_register (io_uring/register.c:1029)
>   do_syscall_64 (arch/x86/entry/syscall_64.c:63
>                  arch/x86/entry/syscall_64.c:94)
>   </TASK>
> 
> The same path is reachable through devmem dmabuf binding via
> netdev_nl_bind_rx_doit() -> net_devmem_bind_dmabuf_to_queue().
> 
> Add a net_iov_init() helper that stamps ->owner, ->type and the
> ->page_type sentinel, and use it from both the devmem and io_uring
> zcrx niov init loops.
> 
> Fixes: db359fccf212 ("mm: introduce a new page type for page pool in page type")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

> ---
> CC: asml.silence@gmail.com
> CC: axboe@kernel.dk
> CC: almasrymina@google.com
> CC: sdf@fomichev.me
> CC: hawk@kernel.org
> CC: akpm@linux-foundation.org
> CC: rppt@kernel.org
> CC: vbabka@kernel.org
> CC: io-uring@vger.kernel.org
> ---
>  include/net/netmem.h | 15 +++++++++++++++
>  io_uring/zcrx.c      |  3 +--
>  net/core/devmem.c    |  3 +--
>  3 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index 507b74c9f52d..78fe51e5756b 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -127,6 +127,21 @@ static inline unsigned int net_iov_idx(const struct net_iov *niov)
>  	return niov - net_iov_owner(niov)->niovs;
>  }
>  
> +/* Initialize a niov: stamp the owning area, the memory provider type,
> + * and the page_type "no type" sentinel expected by the page-type API
> + * (see PAGE_TYPE_OPS in <linux/page-flags.h>) so that
> + * page_pool_set_pp_info() can later call __SetPageNetpp() on a niov
> + * cast to struct page.
> + */
> +static inline void net_iov_init(struct net_iov *niov,
> +				struct net_iov_area *owner,
> +				enum net_iov_type type)
> +{
> +	niov->owner = owner;
> +	niov->type = type;
> +	niov->page_type = UINT_MAX;
> +}
> +
>  /* netmem */
>  
>  /**
> diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
> index 7b93c87b8371..19837e0b5e91 100644
> --- a/io_uring/zcrx.c
> +++ b/io_uring/zcrx.c
> @@ -495,10 +495,9 @@ static int io_zcrx_create_area(struct io_zcrx_ifq *ifq,
>  	for (i = 0; i < nr_iovs; i++) {
>  		struct net_iov *niov = &area->nia.niovs[i];
>  
> -		niov->owner = &area->nia;
> +		net_iov_init(niov, &area->nia, NET_IOV_IOURING);
>  		area->freelist[i] = i;
>  		atomic_set(&area->user_refs[i], 0);
> -		niov->type = NET_IOV_IOURING;
>  	}
>  
>  	if (ifq->dev) {
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index cde4c89bc146..468344739db2 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -297,8 +297,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
>  
>  		for (i = 0; i < owner->area.num_niovs; i++) {
>  			niov = &owner->area.niovs[i];
> -			niov->type = NET_IOV_DMABUF;
> -			niov->owner = &owner->area;
> +			net_iov_init(niov, &owner->area, NET_IOV_DMABUF);
>  			page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov),
>  						      net_devmem_get_dma_addr(niov));
>  			if (direction == DMA_TO_DEVICE)

Re: [PATCH net] net: add net_iov_init() and use it to initialize ->page_type

[Byungchul Park]

On Tue, Apr 28, 2026 at 09:57:08AM +0200, Vlastimil Babka (SUSE) wrote:
> +Cc Byungchul
> 
> On 4/28/26 04:53, Jakub Kicinski wrote:
> > Commit db359fccf212 ("mm: introduce a new page type for page pool in
> > page type") added a page_type field to struct net_iov at the same
> > offset as struct page::page_type, so that page_pool_set_pp_info() can
> > call __SetPageNetpp() uniformly on both pages and net_iovs.
> >
> > The page-type API requires the field to hold the UINT_MAX "no type"
> > sentinel before a type can be set; for real struct page that invariant
> > is established by the page allocator on free. struct net_iov is not
> > allocated through the page allocator, so the field is left as zero

My bad.  Overlooked the point.  Thanks for the fix.

Acked-by: Byungchul Park <byungchul@sk.com>

	Byungchul

> > (io_uring zcrx, which uses __GFP_ZERO) or as slab garbage (devmem,
> > which uses kvmalloc_objs() without zeroing). When the page pool then
> > calls page_pool_set_pp_info() on a freshly-bound niov,
> > __SetPageNetpp()'s VM_BUG_ON_PAGE(page->page_type != UINT_MAX) fires
> > and the kernel BUGs. Triggered in selftests by io_uring zcrx setup
> > through the fbnic queue restart path:
> >
> >  kernel BUG at ./include/linux/page-flags.h:1062!
> >  RIP: 0010:page_pool_set_pp_info (./include/linux/page-flags.h:1062
> >                                   net/core/page_pool.c:716)
> >  Call Trace:
> >   <TASK>
> >   net_mp_niov_set_page_pool (net/core/page_pool.c:1360)
> >   io_pp_zc_alloc_netmems (io_uring/zcrx.c:1089 io_uring/zcrx.c:1110)
> >   fbnic_fill_bdq (./include/net/page_pool/helpers.h:160
> >                   drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:906)
> >   __fbnic_nv_restart (drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2470
> >                       drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2874)
> >   fbnic_queue_start (drivers/net/ethernet/meta/fbnic/fbnic_txrx.c:2903)
> >   netdev_rx_queue_reconfig (net/core/netdev_rx_queue.c:137)
> >   __netif_mp_open_rxq (net/core/netdev_rx_queue.c:234)
> >   io_register_zcrx (io_uring/zcrx.c:818 io_uring/zcrx.c:903)
> >   __io_uring_register (io_uring/register.c:931)
> >   __do_sys_io_uring_register (io_uring/register.c:1029)
> >   do_syscall_64 (arch/x86/entry/syscall_64.c:63
> >                  arch/x86/entry/syscall_64.c:94)
> >   </TASK>
> >
> > The same path is reachable through devmem dmabuf binding via
> > netdev_nl_bind_rx_doit() -> net_devmem_bind_dmabuf_to_queue().
> >
> > Add a net_iov_init() helper that stamps ->owner, ->type and the
> > ->page_type sentinel, and use it from both the devmem and io_uring
> > zcrx niov init loops.
> >
> > Fixes: db359fccf212 ("mm: introduce a new page type for page pool in page type")
> > Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> 
> Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> 
> > ---
> > CC: asml.silence@gmail.com
> > CC: axboe@kernel.dk
> > CC: almasrymina@google.com
> > CC: sdf@fomichev.me
> > CC: hawk@kernel.org
> > CC: akpm@linux-foundation.org
> > CC: rppt@kernel.org
> > CC: vbabka@kernel.org
> > CC: io-uring@vger.kernel.org
> > ---
> >  include/net/netmem.h | 15 +++++++++++++++
> >  io_uring/zcrx.c      |  3 +--
> >  net/core/devmem.c    |  3 +--
> >  3 files changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/net/netmem.h b/include/net/netmem.h
> > index 507b74c9f52d..78fe51e5756b 100644
> > --- a/include/net/netmem.h
> > +++ b/include/net/netmem.h
> > @@ -127,6 +127,21 @@ static inline unsigned int net_iov_idx(const struct net_iov *niov)
> >       return niov - net_iov_owner(niov)->niovs;
> >  }
> >
> > +/* Initialize a niov: stamp the owning area, the memory provider type,
> > + * and the page_type "no type" sentinel expected by the page-type API
> > + * (see PAGE_TYPE_OPS in <linux/page-flags.h>) so that
> > + * page_pool_set_pp_info() can later call __SetPageNetpp() on a niov
> > + * cast to struct page.
> > + */
> > +static inline void net_iov_init(struct net_iov *niov,
> > +                             struct net_iov_area *owner,
> > +                             enum net_iov_type type)
> > +{
> > +     niov->owner = owner;
> > +     niov->type = type;
> > +     niov->page_type = UINT_MAX;
> > +}
> > +
> >  /* netmem */
> >
> >  /**
> > diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
> > index 7b93c87b8371..19837e0b5e91 100644
> > --- a/io_uring/zcrx.c
> > +++ b/io_uring/zcrx.c
> > @@ -495,10 +495,9 @@ static int io_zcrx_create_area(struct io_zcrx_ifq *ifq,
> >       for (i = 0; i < nr_iovs; i++) {
> >               struct net_iov *niov = &area->nia.niovs[i];
> >
> > -             niov->owner = &area->nia;
> > +             net_iov_init(niov, &area->nia, NET_IOV_IOURING);
> >               area->freelist[i] = i;
> >               atomic_set(&area->user_refs[i], 0);
> > -             niov->type = NET_IOV_IOURING;
> >       }
> >
> >       if (ifq->dev) {
> > diff --git a/net/core/devmem.c b/net/core/devmem.c
> > index cde4c89bc146..468344739db2 100644
> > --- a/net/core/devmem.c
> > +++ b/net/core/devmem.c
> > @@ -297,8 +297,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
> >
> >               for (i = 0; i < owner->area.num_niovs; i++) {
> >                       niov = &owner->area.niovs[i];
> > -                     niov->type = NET_IOV_DMABUF;
> > -                     niov->owner = &owner->area;
> > +                     net_iov_init(niov, &owner->area, NET_IOV_DMABUF);
> >                       page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov),
> >                                                     net_devmem_get_dma_addr(niov));
> >                       if (direction == DMA_TO_DEVICE)

Re: [PATCH net] net: add net_iov_init() and use it to initialize ->page_type

[Jens Axboe]

On 4/27/26 8:53 PM, Jakub Kicinski wrote:
> Commit db359fccf212 ("mm: introduce a new page type for page pool in
> page type") added a page_type field to struct net_iov at the same
> offset as struct page::page_type, so that page_pool_set_pp_info() can
> call __SetPageNetpp() uniformly on both pages and net_iovs.

Thanks for catching that, that's an oversight in the offending commit.

Reviewed-by: Jens Axboe <axboe@kernel.dk>

-- 
Jens Axboe