Re: [PATCH 0/6] virtio-iommu: Add ACPI support

[Eric Auger <eric.auger@redhat.com>]

Hi Jean,

On 8/27/21 3:30 PM, Jean-Philippe Brucker wrote:
> Hi Eric,
>
> On Tue, Aug 17, 2021 at 04:58:01PM +0200, Eric Auger wrote:
>> Hi Jean,
>>
>> On 8/10/21 10:45 AM, Jean-Philippe Brucker wrote:
>>> Allow instantiating a virtio-iommu device on ACPI systems by adding a
>>> Virtual I/O Translation table (VIOT). Enable x86 support for VIOT.
>> Don't you need your other patch
>> "virtio-iommu: Default to bypass during boot"?
>>
>> Without this latter, for me the guest fails to boot.
> Good point, I think I've been lucky during my testing. My bootloader and
> kernel are on virtio-blk-pci devices and as I wasn't explicitly enabling
> the "iommu_platform" parameter, they would bypass the IOMMU. When enabling
> the parameter, boot hangs since the IOMMU isn't enabled when the
> bootloader needs to fetch the kernel, and DMA faults. That parameter is
> specific to virtio devices. Using another storage for bootloader and
> kernel will result in failure to boot.
>
> I've been postponing the boot-bypass patch since it requires a
> specification change to be done right, but it's next on my list.
The boot-bypass feature seems a critical feature to overcome the current
v3 limitation. Are there big spec changes required? Maybe we shall work
on this in parallel of this series because, to me, it will delay the
integration of virtio-iommu in libvirt for instance.

Thanks

Eric
>
> Thanks,
> Jean
>