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

From: Andy Lutomirski
Subject: Re: [Qemu-devel] [PATCH V2 RFC] fixup! virtio: convert to use DMA api
Date: Wed, 27 Apr 2016 07:31:43 -0700

On Wed, Apr 27, 2016 at 7:23 AM, Joerg Roedel <address@hidden> wrote:
> 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.

Except on PPC and SPARC.  As far as I know, those are the only
problematic platforms.

Is it too late to *disable* QEMU's q35-iommu thingy until it can be
fixed to report correct data in the DMAR tables?


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