Re: Device pass through on XEN on ARM

["Khandelwal, Shubham" <Shubham.Khandelwal@harman.com>]

Hello Ian,

On 06/11/2014 03:13 PM, Ian Campbell wrote:
> > Just to try out the passthrough using the hacks you mentioned, I made
> > changes in xen to assign a GPIO controlled LED to domU by calling
> > map_mmio_regions() in the domain creation path. After domU boots, when
> > I try to access the LED using ioremap, ioread and iowrite from kernel
> > space I see that I am not able to control the LED,

> How does it fail? Does it give a fault in the hypervisor or the guest
> kernel or just silently eat the MMIO writes and not do anything?

There is a panic in the guest kernel


> 0x4xxxxxxx is a RAM region on 4.5 (see the end of
> xen/include/public/arch-arm.h), I suspect your mmio mapping is being
> clobbered by a RAM mapping (and therefore that your answer above is
> "silently does nothing".

I just checked xen/include/public/arch-arm.h Line 372 is 

#define GUEST_RAM_BASE    0x80000000ULL

So as per my understanding 0x4xxxxxxx is not a ram region and thus there should not be any clobbering.


> Do you need this to be a 1:1 mapping or could you move it to some free
> space? Most of the low GB is free (but do check arch-arm.h) to be used
> for MMIO mappings.

I do not necessarily need it to be a 1:1 mapping.

> Ian.

Regards

Shubham Khandelwal