Re: IOMMU problem on Xen dom0 arm (Was: Re: Xen on arm Chromebook seems to cause no display on screen)

[Julien Grall <julien@xxxxxxx>]

Hi Chuck,

On 27/10/2023 00:26, Chuck Zmudzinski wrote:
> On 10/26/2023 5:24 PM, Julien Grall wrote:
> > Anyway, letting dom0 to use the IOMMU is probably a bad idea as even if
> > dom0 memory is direct mapped, grant mappings are not. So you would end
> > up to see random crashes.
> I noticed some possible relevant settings from my Linux config:
>
> CONFIG_XEN_GNTDEV=m
> CONFIG_XEN_GRANT_DEV_ALLOC=m
> # CONFIG_XEN_GRANT_DMA_ALLOC is not set
>
> I also have in my dom0 config:
>
> # CONFIG_XEN_VIRTIO is not set
>
> Also, not even mentioned in my Linux config but option is available in
> Linux, but it can be enabled by enabling CONFIG_XEN_VIRTIO in the
> configuration stage of the Linux build:
>
> # CONFIG_XEN_GRANT_DMA_IOMMU is not set
>
> Is virtio a safe way to provide IOMMU support for dom0? Maybe I can
> enable this and see if it helps, but will it cause random crashes?
None of the options above matter to boot dom0. They are related to PV 
functionality on both the backend and frontend side.
Cheers,


--
Julien Grall