Re: [PATCH net] net: stmmac: fix TSO DMA API usage causing oops

[Furong Xu <0x1207@gmail.com>]

On Fri, 06 Dec 2024 12:40:11 +0000, "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk> wrote:

> Commit 66600fac7a98 ("net: stmmac: TSO: Fix unbalanced DMA map/unmap
> for non-paged SKB data") moved the assignment of tx_skbuff_dma[]'s
> members to be later in stmmac_tso_xmit().
> 
> The buf (dma cookie) and len stored in this structure are passed to
> dma_unmap_single() by stmmac_tx_clean(). The DMA API requires that
> the dma cookie passed to dma_unmap_single() is the same as the value
> returned from dma_map_single(). However, by moving the assignment
> later, this is not the case when priv->dma_cap.addr64 > 32 as "des"
> is offset by proto_hdr_len.
> 
> This causes problems such as:
> 
>   dwc-eth-dwmac 2490000.ethernet eth0: Tx DMA map failed
> 
> and with DMA_API_DEBUG enabled:
> 
>   DMA-API: dwc-eth-dwmac 2490000.ethernet: device driver tries to +free DMA memory it has not allocated [device address=0x000000ffffcf65c0] [size=66 bytes]
> 
> Fix this by maintaining "des" as the original DMA cookie, and use
> tso_des to pass the offset DMA cookie to stmmac_tso_allocator().
> 
> Full details of the crashes can be found at:
> https://lore.kernel.org/all/d8112193-0386-4e14-b516-37c2d838171a@nvidia.com/
> https://lore.kernel.org/all/klkzp5yn5kq5efgtrow6wbvnc46bcqfxs65nz3qy77ujr5turc@bwwhelz2l4dw/
> 
> Reported-by: Jon Hunter <jonathanh@nvidia.com>
> Reported-by: Thierry Reding <thierry.reding@gmail.com>
> Fixes: 66600fac7a98 ("net: stmmac: TSO: Fix unbalanced DMA map/unmap for non-paged SKB data")

Much appreciated for this fix.

Reviewed-by: Furong Xu <0x1207@gmail.com>