RE: [PATCH net] net: mana: Sync page pool RX frags for CPU

[Haiyang Zhang]

> -----Original Message-----
> From: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Sent: Wednesday, June 17, 2026 11:50 PM
> To: KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; wei.liu@xxxxxxxxxx; Dexuan Cui
> <DECUI@xxxxxxxxxxxxx>; Long Li <longli@xxxxxxxxxxxxx>;
> andrew+netdev@xxxxxxx; davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx;
> kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx; Konstantin Taranov
> <kotaranov@xxxxxxxxxxxxx>; horms@xxxxxxxxxx; ernis@xxxxxxxxxxxxxxxxxxx;
> dipayanroy@xxxxxxxxxxxxxxxxxxx; kees@xxxxxxxxxx; jacob.e.keller@xxxxxxxxx;
> ssengar@xxxxxxxxxxxxxxxxxxx; linux-hyperv@xxxxxxxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> rdma@xxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Subject: [PATCH net] net: mana: Sync page pool RX frags for CPU
> 
> MANA allocates RX buffers from page pool fragments when frag_count is
> greater than 1. In that case the buffers remain DMA mapped by page pool
> and the RX completion path does not call dma_unmap_single(). As a result,
> the implicit sync-for-CPU normally performed by dma_unmap_single() is
> missing before the packet data is passed to the networking stack.
> 
> This breaks RX on configurations which require explicit DMA syncing, for
> example when booted with swiotlb=force.
> 
> Fix this by recording the page pool page and DMA sync offset when the RX
> buffer is allocated, and syncing the received packet range for CPU access
> before handing the RX buffer to the stack.
> 
> Also validate the packet length reported in the RX CQE before using it as
> a DMA sync length or passing it to skb processing. The CQE is supplied
> by the device and should not be blindly trusted by Confidential VMs.
> 
> Fixes: 730ff06d3f5c ("net: mana: Use page pool fragments for RX buffers
> instead of full pages to improve memory efficiency.")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> ---
>  drivers/net/ethernet/microsoft/mana/mana_en.c | 61 +++++++++++++++----
>  include/net/mana/mana.h                       |  8 +++
>  2 files changed, 57 insertions(+), 12 deletions(-)

Reviewed-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>