linux-kernel - Re: [PATCH RFC] fixup! virtio: convert to use DMA api

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Date:	Mon, 18 Apr 2016 10:03:52 -0400
From:	David Woodhouse <dwmw2@...radead.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	qemu-devel@...gnu.org, linux-kernel@...r.kernel.org,
	pbonzini@...hat.com, peterx@...hat.com, cornelia.huck@...ibm.com,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Kevin Wolf <kwolf@...hat.com>,
	Amit Shah <amit.shah@...hat.com>, qemu-block@...gnu.org,
	Jason Wang <jasowang@...hat.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Wei Liu <wei.liu2@...rix.com>,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org
Subject: Re: [PATCH RFC] fixup! virtio: convert to use DMA api

On Mon, 2016-04-18 at 16:12 +0300, Michael S. Tsirkin wrote:
> I'm not sure I understand the issue.  The public API is not about how
> the driver works.  It doesn't say "don't use DMA API" anywhere, does it?
> It's about telling device whether to obey the IOMMU and
> about discovering whether a device is in fact under the IOMMU.

Apologies, I was wrongly reading this as a kernel patch.

After a brief struggle with "telling device whether to obey the IOMMU",
which is obviously completely impossible from the guest kernel, I
realise my mistake :)

So... on x86 how does this get reflected in the DMAR tables that the
guest BIOS presents to the guest kernel, so that the guest kernel
*knows* which devices are behind which IOMMU?

(And are you fixing the case of assigned PCI devices, which aren't
behind any IOMMU, at the same time as you answer that? :)

-- 
dwmw2



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