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

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

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
> path.
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 permission.
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.
Cheers,

--
Julien Grall