Re: [PATCH v4 07/15] iommu/vt-d: Delegate the dma domain to upper layer

[Lu Baolu]

Hi Chris,

On 2020/8/22 2:33, Chris Wilson wrote:
> Quoting Lu Baolu (2019-05-25 06:41:28)
> > This allows the iommu generic layer to allocate a dma domain and
> > attach it to a device through the iommu api's. With all types of
> > domains being delegated to upper layer, we can remove an internal
> > flag which was used to distinguish domains mananged internally or
> > externally.
>
> I'm seeing some really strange behaviour with this patch on a 32b
> Skylake system (and still present on mainline). Before this patch
> everything is peaceful and appears to work correctly. Applying this patch,
> and we fail to initialise the GPU with a few DMAR errors reported, e.g.
>
> [   20.279445] DMAR: DRHD: handling fault status reg 3
> [   20.279508] DMAR: [DMA Read] Request device [00:02.0] fault addr 8900a000 [fault reason 05] PTE Write access is not set
>
> Setting an identity map for the igfx made the DMAR errors disappear, but
> the GPU still failed to initialise.
>
> There's no difference in the DMAR configuration dmesg between working and
> the upset patch. And the really strange part is that switching to a 64b
> kernel with this patch, it's working.
>
> Any suggestions on what I should look for?

Can the patch titled "[PATCH] iommu/intel: Handle 36b addressing for
x86-32" solve this problem?

Best regards,
baolu