Subject: Re: tg3 NIC driver bug in 3.14.x under Xen [and 3 more messages]

From: Prashant Sreedharan <[email-masked]>
Date: Thu, 16 Apr 2015 15:51:34 -0700

On Thu, 2015-04-16 at 18:15 +0100, Ian Jackson wrote:
> Michael Chan writes ("Re: tg3 NIC driver bug in 3.14.x under Xen [and 3 more messages]"):
> > On Thu, 2015-04-16 at 09:24 -0300, [email-masked] wrote: 
> > > Yes, this looks like the driver is not syncing the DMA buffers. Unmap is
> > > supposed to synchronize as well.
> > 
> > For small rx packets (< 256 bytes), we sync the DMA buffer before we
> > copy the data to another SKB.  For larger packets, we unmap the DMA
> > buffer.  Do we see the corruption in both cases?
> 
> Yes, at least with swiotlb=force iommu=soft.

Ok this is what is causing the problem, the driver uses
DEFINE_DMA_UNMAP_ADDR(), dma_unmap_addr_set() to keep a copy of the dma
"mapping" and dma_unmap_addr() to get the "mapping" value. On most of
the platforms this is a no-op, but it appears with "iommu=soft and
swiotlb=force" this house keeping is required, when I pass the correct
dma_addr instead of 0 while calling pci_unmap_/pci_dma_sync_ I don't see
the corruption. ie If you set CONFIG_NEED_DMA_MAP_STATE=y in your kernel
config you should not see the problem. Can you confirm ? Thanks