lan966x_fdma_reload() backs up rx->page_pool and rx->fdma before
reallocating the RX resources for the new MTU. If the allocation fails,
the restore path puts these fields back before restarting RX.

However, the reload path also updates rx->page_order and rx->max_mtu
before calling lan966x_fdma_rx_alloc(). These fields are not restored on
failure, so RX can be restarted with the old pages, old FDMA state and
old page pool, but with the page geometry from the failed new MTU.

This can make the XDP path advertise a frame size derived from the new
page_order while the actual RX pages still come from the old allocation.
For example, after a failed reload to a jumbo MTU, xdp_init_buff() may be
called with a frame size larger than the restored RX pages.

lan966x_fdma_rx_alloc_page_pool() also registers the newly allocated page
pool with each port's XDP RXQ before fdma_alloc_coherent() is called. If
fdma_alloc_coherent() fails, the new page pool is destroyed, but the
rollback path does not restore the per-port XDP RXQ mem model
registration either.

Save and restore rx->page_order and rx->max_mtu, and restore the old page
pool registration for each port's XDP RXQ before RX is started again.
This keeps the restored RX state consistent after a failed reload.

Fixes: 59c3d55a946c ("net: lan966x: fix use-after-free and leak in lan966x_fdma_reload()")
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
---
v2:
  - Save and restore rx->page_order and rx->max_mtu in the reload rollback
    path.
  - Keep the XDP RXQ page-pool registration restore from v1.

 .../ethernet/microchip/lan966x/lan966x_fdma.c | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
index f8ce735a7fc0..8272ad085150 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
@@ -815,6 +815,7 @@ static int lan966x_fdma_reload(struct lan966x *lan966x, int new_mtu)
 	struct page *(*old_pages)[FDMA_RX_DCB_MAX_DBS];
 	struct page_pool *page_pool;
 	struct fdma fdma_rx_old;
+	int page_order, max_mtu;
 	int err, i, j;
 
 	old_pages = kmemdup(lan966x->rx.page, sizeof(lan966x->rx.page),
@@ -825,6 +826,8 @@ static int lan966x_fdma_reload(struct lan966x *lan966x, int new_mtu)
 	/* Store these for later to free them */
 	memcpy(&fdma_rx_old, &lan966x->rx.fdma, sizeof(struct fdma));
 	page_pool = lan966x->rx.page_pool;
+	page_order = lan966x->rx.page_order;
+	max_mtu = lan966x->rx.max_mtu;
 
 	napi_synchronize(&lan966x->napi);
 	napi_disable(&lan966x->napi);
@@ -854,7 +857,24 @@ static int lan966x_fdma_reload(struct lan966x *lan966x, int new_mtu)
 	return 0;
 restore:
 	lan966x->rx.page_pool = page_pool;
+	lan966x->rx.page_order = page_order;
+	lan966x->rx.max_mtu = max_mtu;
 	memcpy(&lan966x->rx.fdma, &fdma_rx_old, sizeof(struct fdma));
+	/*
+	 * lan966x_fdma_rx_alloc_page_pool() registered the new pool with
+	 * each port's XDP RXQ before the allocation failed. The new pool is
+	 * destroyed by lan966x_fdma_rx_alloc(), so restore the old pool's
+	 * registration before restarting RX.
+	 */
+	for (i = 0; i < lan966x->num_phys_ports; i++) {
+		if (!lan966x->ports[i])
+			continue;
+
+		xdp_rxq_info_unreg_mem_model(&lan966x->ports[i]->xdp_rxq);
+		xdp_rxq_info_reg_mem_model(&lan966x->ports[i]->xdp_rxq,
+					   MEM_TYPE_PAGE_POOL, page_pool);
+	}
+
 	lan966x_fdma_rx_start(&lan966x->rx);
 
 	lan966x_fdma_wakeup_netdev(lan966x);
-- 
2.43.0

ACK on the code part at least, maintainers might disagree with this:
changelog could also note the subject rename ("restore XDP RXQ page
pool" -> "restore RX state"), so the scope change from v1 is obvious
but that s a very minor nit IMO.

Reviewed-by: David Carlier <devnexen@gmail.com>

On Sun, 7 Jun 2026 at 15:58, Guangshuo Li <lgs201920130244@gmail.com> wrote:
>
> lan966x_fdma_reload() backs up rx->page_pool and rx->fdma before
> reallocating the RX resources for the new MTU. If the allocation fails,
> the restore path puts these fields back before restarting RX.
>
> However, the reload path also updates rx->page_order and rx->max_mtu
> before calling lan966x_fdma_rx_alloc(). These fields are not restored on
> failure, so RX can be restarted with the old pages, old FDMA state and
> old page pool, but with the page geometry from the failed new MTU.
>
> This can make the XDP path advertise a frame size derived from the new
> page_order while the actual RX pages still come from the old allocation.
> For example, after a failed reload to a jumbo MTU, xdp_init_buff() may be
> called with a frame size larger than the restored RX pages.
>
> lan966x_fdma_rx_alloc_page_pool() also registers the newly allocated page
> pool with each port's XDP RXQ before fdma_alloc_coherent() is called. If
> fdma_alloc_coherent() fails, the new page pool is destroyed, but the
> rollback path does not restore the per-port XDP RXQ mem model
> registration either.
>
> Save and restore rx->page_order and rx->max_mtu, and restore the old page
> pool registration for each port's XDP RXQ before RX is started again.
> This keeps the restored RX state consistent after a failed reload.
>
> Fixes: 59c3d55a946c ("net: lan966x: fix use-after-free and leak in lan966x_fdma_reload()")
> Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
> ---
> v2:
>   - Save and restore rx->page_order and rx->max_mtu in the reload rollback
>     path.
>   - Keep the XDP RXQ page-pool registration restore from v1.
>
>  .../ethernet/microchip/lan966x/lan966x_fdma.c | 20 +++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> index f8ce735a7fc0..8272ad085150 100644
> --- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> @@ -815,6 +815,7 @@ static int lan966x_fdma_reload(struct lan966x *lan966x, int new_mtu)
>         struct page *(*old_pages)[FDMA_RX_DCB_MAX_DBS];
>         struct page_pool *page_pool;
>         struct fdma fdma_rx_old;
> +       int page_order, max_mtu;
>         int err, i, j;
>
>         old_pages = kmemdup(lan966x->rx.page, sizeof(lan966x->rx.page),
> @@ -825,6 +826,8 @@ static int lan966x_fdma_reload(struct lan966x *lan966x, int new_mtu)
>         /* Store these for later to free them */
>         memcpy(&fdma_rx_old, &lan966x->rx.fdma, sizeof(struct fdma));
>         page_pool = lan966x->rx.page_pool;
> +       page_order = lan966x->rx.page_order;
> +       max_mtu = lan966x->rx.max_mtu;
>
>         napi_synchronize(&lan966x->napi);
>         napi_disable(&lan966x->napi);
> @@ -854,7 +857,24 @@ static int lan966x_fdma_reload(struct lan966x *lan966x, int new_mtu)
>         return 0;
>  restore:
>         lan966x->rx.page_pool = page_pool;
> +       lan966x->rx.page_order = page_order;
> +       lan966x->rx.max_mtu = max_mtu;
>         memcpy(&lan966x->rx.fdma, &fdma_rx_old, sizeof(struct fdma));
> +       /*
> +        * lan966x_fdma_rx_alloc_page_pool() registered the new pool with
> +        * each port's XDP RXQ before the allocation failed. The new pool is
> +        * destroyed by lan966x_fdma_rx_alloc(), so restore the old pool's
> +        * registration before restarting RX.
> +        */
> +       for (i = 0; i < lan966x->num_phys_ports; i++) {
> +               if (!lan966x->ports[i])
> +                       continue;
> +
> +               xdp_rxq_info_unreg_mem_model(&lan966x->ports[i]->xdp_rxq);
> +               xdp_rxq_info_reg_mem_model(&lan966x->ports[i]->xdp_rxq,
> +                                          MEM_TYPE_PAGE_POOL, page_pool);
> +       }
> +
>         lan966x_fdma_rx_start(&lan966x->rx);
>
>         lan966x_fdma_wakeup_netdev(lan966x);
> --
> 2.43.0
>