Re: [PATCH v4 00/33] xen/arm: Add support for non-PCI passthrough

[Julien Grall <julien.grall@linaro.org>]

On 20/03/2015 01:22, Edgar E. Iglesias wrote:
> Hi Julien,

Hello Edgar,

> The partial device-tree support is nice and very flexible. I couldn't help
> thinking that it would be nice to be able to describe more of the
> guest with device-trees. It may be controversial but it would be cool
> to be able to go:
>
> xl create my-guest.dtb

While it would be feasible to move some part of the IRQ/MMIO pass-thru 
in the device tree, there is some configuration options (such as the 
vif, the kernel...) that can't be easily be described in the 
configuration file.

> A more down-to earth thing I ran into is that on the ZynqMP, the Cortex-A53
> is setup to have 40 bits physical addresses. Our SMMU announces support
> for up to 48bit input addresses (but can be configured for 40bits
> aswell).
>
> When XEN sets up passthrough for a dev, it probes the SMMU for the
> max input address size and uses that as the input size for the
> context. But because XEN reuses the page tables from p2m for the
> SMMU, we end up in a miss-match.
>
> I haven't looked at the details of how to fix but my gut feeling
> is that we should be re-using the input size of the stage 2
> page-tables as the input-size for the SMMU.
> And only use the max input size of the SMMU to assert that it
> is big enough. I may be missing something though.

> The code in question is at the end of arm_smmu_device_cfg_probe(),
> already merged.

You are right, we should take into account the size of the CPU physical 
address.

Re-using the input size of the stage 2 page-tables seems the best solution.

Although, if I'm not mistaken, I have the inverse problem on one of our 
board. I.e the input-size of the SMMU is too small. I need to double check.

Regards,

-- 
Julien Grall