Re: [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API

Paolo Bonzini
2014-09-03T15:11:45Z

Il 03/09/2014 17:07, Andy Lutomirski ha scritto:
>> > Yes, only for virtio---but for x86 I think it should be off by default,
>> > even if that means virtio+IOMMU requires a new kernel.
> Just to clarify: is "it" the direct-ram-access property? If so, I
> think I might agree.

Yes.

> Alternatively, could QEMU easily teach the IOMMU code to generate the
> ACPI tables such that virtio-pci devices aren't advertised as living
> behind the IOMMU? This would work both with and without my patches.
> On the other hand, maybe this gets complicated when hotplug is
> involved.

That could be possible. For hot-plug, you can simply forbid hotplugging
with direct-ram-access=on. If you want hotplug, then we should add the
direct-ram-access property to PCI bridges too (with the same limitation
on hotplug). All devices under such a bridge would be outside the
IOMMU, including virtio devices with direct-ram-access=off.

Paolo