Re: [Xen-devel] xen/arm: Hiding SMMUs from Dom0 when using ACPI on Xen

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

Hi Julien,

On Wed, Feb 22, 2017 at 7:40 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> Hello,
>
> There was few discussions recently about hiding SMMUs from DOM0 when using
> ACPI. I thought it would be good to have a separate thread for this.
>
> When using ACPI, the SMMUs will be described in the IO Remapping Table
> (IORT). The specification can be found on the ARM website [1].
>
> For a brief summary, the IORT can be used to discover the SMMUs present on
> the platform and find for a given device the ID to configure components such
> as ITS (DeviceID) and SMMU (StreamID).
>
> The appendix A in the specification gives an example how DeviceID and
> StreamID can be found. For instance, when a PCI device is both protected by
> an SMMU and MSI-capable the following translation will happen:
>         RID -> StreamID -> DeviceID
>
> Currently, SMMUs are hidden from DOM0 because they are been used by Xen and
> we don't support stage-1 SMMU. If we pass the IORT as it is, DOM0 will try
> to initialize SMMU and crash.
>
> I first thought about using a Xen specific way (STAO) or extending a flag in
> IORT. But that is not ideal.
>
> So we would have to rewrite the IORT for DOM0. Given that a range of RID can
> mapped to multiple ranges of DeviceID, we would have to translate RID one by
> one to find the associated DeviceID. I think this may end up to complex code
> and have a big IORT table.

Why can't we replace Output base of IORT of PCI node with SMMU output base?.
I mean similar to PCI node without SMMU, why can't replace output base
of PCI node with
SMMU's output base?.

The issue I see is RID is [15:0] where is DeviceID is [17:0].

>
> However, given that DeviceID will be used by DOM0 to only configure the ITS.
> We have no need to use to have the DOM0 DeviceID equal to the host DeviceID.
> So I think we could simplify our life by generating DeviceID for each RID
> range.

If DOM0 DeviceID != host Device ID, then we cannot initialize ITS using DOM0
ITS commands (MAPD). So, is it concluded that ITS initializes all the devices
with platform specific Device ID's in Xen?.

>
> Any opinions?
>
> Cheers,
>
> [1]
> http://infocenter.arm.com/help/topic/com.arm.doc.den0049b/DEN0049B_IO_Remapping_Table.pdf
>
> --
> Julien Grall
>
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