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Re: [Qemu-devel] [PATCH V2 RFC] fixup! virtio: convert to use DMA api

From: Joerg Roedel
Subject: Re: [Qemu-devel] [PATCH V2 RFC] fixup! virtio: convert to use DMA api
Date: Wed, 27 Apr 2016 16:23:32 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

On Wed, Apr 27, 2016 at 04:37:04PM +0300, Michael S. Tsirkin wrote:
> One correction: it's a feature of the device in the system.
> There could be a mix of devices bypassing and not
> bypassing the IOMMU.

No, it really is not. A device can't chose to bypass the IOMMU. But the
IOMMU can chose to let the device bypass. So any fix here belongs
into the platform/iommu code too and not into some driver.

> Sounds good. And a way to detect appropriate devices could
> be by looking at the feature flag, perhaps?

Again, no! The way to detect that is to look into the iommu description
structures provided by the firmware. They provide everything necessary
to tell the iommu code which devices are not translated.


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