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

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Date:	Fri, 17 Apr 2015 13:19:56 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	Ian.Jackson@...citrix.com
Cc:	prashant@...adcom.com, mchan@...adcom.com,
	cascardo@...ux.vnet.ibm.com, konrad.wilk@...cle.com,
	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	vyasevich@...il.com, xen-devel@...ts.xensource.com,
	netdev@...r.kernel.org, siva.kallam@...adcom.com,
	sanjeevb@...adcom.com
Subject: Re: tg3 NIC driver bug in 3.14.x under Xen [and 3 more messages]

From: Ian Jackson <Ian.Jackson@...citrix.com>
Date: Fri, 17 Apr 2015 17:29:28 +0100

> Prashant Sreedharan writes ("Re: tg3 NIC driver bug in 3.14.x under Xen [and 3 more messages]"):
>> 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
> 
> That kernel config option is an automatically computed one:
> 
> config NEED_DMA_MAP_STATE
>         def_bool y
>         depends on X86_64 || INTEL_IOMMU || DMA_API_DEBUG
> 
> and grepping my .config shows:
> 
> # CONFIG_INTEL_IOMMU is not set
> # CONFIG_DMA_API_DEBUG is not set
> 
> It's a 32-bit kernel so it hasn't got X86_64 enabled either.
> 
> Arguably at least some of osstest's kernels should have INTEL_IOMMU
> enabled to detect conflicts between Xen's use of the iommu and
> possible attempts bo Linux to do the same thing, but not having it
> enabled should not cause a driver bug.

So the gist of the situation is, that NEED_DMA_MAP_STATE can be 'n' in
situations where we might actually need it to be 'y' based upon kernel
comman line boot options given.

Right?
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