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 17:29:28 +0100
From:	Ian Jackson <Ian.Jackson@...citrix.com>
To:	Prashant Sreedharan <prashant@...adcom.com>
CC:	Michael Chan <mchan@...adcom.com>, <cascardo@...ux.vnet.ibm.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	"Vlad Yasevich" <vyasevich@...il.com>,
	<xen-devel@...ts.xensource.com>, <netdev@...r.kernel.org>,
	"Siva Reddy (Siva) Kallam" <siva.kallam@...adcom.com>,
	Sanjeev Bansal <sanjeevb@...adcom.com>
Subject: Re: tg3 NIC driver bug in 3.14.x under Xen [and 3 more messages]

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.

Ian.
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