On Thu, Aug 12, 2021 at 1:05 PM Marc Zyngier [off-list ref] wrote:

On Thu, 12 Aug 2021 11:18:35 +0100,
Matteo Croce [off-list ref] wrote:

quoted

On Thu, 12 Aug 2021 10:48:03 +0200
Eric Dumazet [off-list ref] wrote:

quoted

On 8/11/21 4:16 PM, Marc Zyngier wrote:

quoted

On Wed, 11 Aug 2021 13:53:59 +0100,
Eric Dumazet [off-list ref] wrote:

quoted

Are you sure you do not need to adjust stmmac_set_bfsize(),
stmmac_rx_buf1_len() and stmmac_rx_buf2_len() ?

Presumably DEFAULT_BUFSIZE also want to be increased by NET_SKB_PAD

Patch for stmmac_rx_buf1_len() :

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index
7b8404a21544cf29668e8a14240c3971e6bce0c3..041a74e7efca3436bfe3e17f972dd156173957a9
100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++
b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -4508,12
+4508,12 @@ static unsigned int stmmac_rx_buf1_len(struct
stmmac_priv *priv, /* First descriptor, not last descriptor and
not split header */ if (status & rx_not_ls)
-               return priv->dma_buf_sz;
+               return priv->dma_buf_sz - NET_SKB_PAD -
NET_IP_ALIGN;
        plen = stmmac_get_rx_frame_len(priv, p, coe);

        /* First descriptor and last descriptor and not split
header */
-       return min_t(unsigned int, priv->dma_buf_sz, plen);
+       return min_t(unsigned int, priv->dma_buf_sz - NET_SKB_PAD
- NET_IP_ALIGN, plen); }

 static unsigned int stmmac_rx_buf2_len(struct stmmac_priv *priv,

Feels like a major deficiency of the original patch. Happy to test a
more complete patch if/when you have one.

I wont have time in the immediate future.

Matteo, if you do not work on a fix, I suggest we revert
 a955318fe67ec0d962760b5ee58e74bffaf649b8 stmmac: align RX buffers

before a more polished version can be submitted.

Better to use stmmac_rx_offset() so to have the correct length when
using XDP. Also, when XDP is enabled, the offset was
XDP_PACKET_HEADROOM (i.e. 256 bytes) even before the change, so it
could be already broken. Mark, can you try on the Jetson TX2 by
attaching an XDP program and see if it works without my change?

Sorry, you'll have to hold my hand here, as I know exactly nothing
about XDP....

Attach the attached object with:

ip link set eth0 xdp object passall.o

This is an empty XDP program, its source:

__attribute__((section("prog"), used))
int xdp_main(struct xdp_md *ctx)
{
       return XDP_PASS;
}

Every packet will pass untouched, but the offset will be shifted from
0 to 256 bytes, which could trigger the problem anyway:

quoted

A possible fix, which takes in account also the XDP headroom for
stmmac_rx_buf1_len() only could be (only compile tested, I don't have
the hardware now):

However, this doesn't fix my issue. I still get all sort of
corruption. Probably stmmac_rx_buf2_len() also need adjusting (it has
a similar logic as its buf1 counterpart...)

Unless you can fix it very quickly, and given that we're towards the
end of the cycle, I'd be more comfortable if we reverted this patch.

Can it be that the HW can't do DMA on an address which is not word aligned?
What if you replace NET_SKB_PAD with, let's say, 8?

Regards,
-- 
per aspera ad upstream