linux-kernel - Re: [PATCH v3 0/3] virtio DMA API core stuff

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Message-ID: <1448207661.89124.50.camel@infradead.org>
Date:	Sun, 22 Nov 2015 15:54:21 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	marcel@...hat.com, Joerg Roedel <jroedel@...e.de>,
	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-s390 <linux-s390@...r.kernel.org>, KVM <kvm@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Andy Lutomirski <luto@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Christoph Hellwig <hch@....de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff

On Sun, 2015-11-22 at 15:06 +0200, Marcel Apfelbaum wrote:
> 
> 
> I tried to generate a DMAR table that excludes some devices from
> IOMMU translation, however it does not help.
> 
> The reason is, as far as I understand, that Linux kernel does
> not allow any device being outside an IOMMU scope if the
> iommu kernel option is activated.
> 
> Does anybody know if it is "by design" or is simply an uncommon
> configuration?
> (some devices in an IOMMU scope, while others outside *any* IOMMU
> scope)

That's a kernel bug in the way it handles per-device DMA operations. Or
more to the point, in the way it doesn't — the non-translated devices
end up being pointed to the intel_dma_ops despite the fact they
shouldn't be. I'm working on that...

-- 
dwmw2


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