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Re: [PATCH 12/12] xen/arm: call iomem_permit_access for passthrough devices

Hi Stefano,

On 26/05/2020 17:46, Stefano Stabellini wrote:
On Sun, 24 May 2020, Julien Grall wrote:
On 30/04/2020 14:01, Julien Grall wrote:
On 29/04/2020 21:47, Stefano Stabellini wrote:
On Wed, 15 Apr 2020, Julien Grall wrote: But doesn't it make sense to give
domU permission if it is going to get
the memory mapped? But admittedly I can't think of something that would
break because of the lack of the iomem_permit_access call in this code

On Arm, the permissions are only useful if you plan you DomU to delegate the
regions to another domain. As your domain is not even aware it is running on
Xen (we don't expose 'xen' node in the DT), it makes little sense to add the

I actually found one use when helping a user last week. You can dump the list
of MMIO regions assigned to a guest from Xen Console.

This will use d->iomem_caps that is modified via iomem_permit_access().
Without it, there is no easy way to confirm the list of MMIO regions assigned
to a guest. Although...

Even today, you can map IOMEM to a DomU and then revert the permission right
after. They IOMEM will still be mapped in the guest and it will act normaly.

... this would not help the case where permissions are reverted. But I am
assuming this shouldn't happen for Dom0less.

Thank you for looking into this

Stefano, I am not sure what's your plan for the series itself for Xen 4.14. I
think this patch could go in now. Any thoughts?

For the series: I have addresses all comments in my working tree except
for the ones on memory allocation (the thread "xen: introduce
reserve_heap_pages"). It looks like that part requires a complete
rewrite, and it seems that the new code is not trivial to write. So I am
thinking of not targeting 4.14. What do you think? Do you think the new
code should be "easy" enough that I could target 4.14?
It may be a stretch with the code freeze on Friday. I would suggest to send it when it is ready and we can either include in Xen 4.14 or as soon as the tree re-open.

For this patch: it is fine to go in now, doesn't have to wait for the

Feel free to add my ack on the patch.


Julien Grall



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