Re: [Xen-users] Debugging DomU

["Chris (Christopher) Brand" <chris.brand@xxxxxxxxxxxx>]

Hi Julien,

>This is normal that address 0 is not mapped to any RAM. The memory layout of 
>the guest (see xen/include/public/arch-arm.h) as the RAM guest defined in 
>higher memory.
Ok. That seems to match what I'm seeing in the MMU - VTTBR for that guest 
contains two L1 tables, one at 0 and one at 0x40000000 (GUEST_RAM_BASE). The 
first is almost empty while the second has quite a few mappings. I assume VTTBR 
is where I should be looking ?

>Although, vmlinux is using virtual address, so 0 is likely a virtual address. 
>Do you know if the page table has been setup to the guest?
I see a call to p2m_alloc_table(), followed by a number of calls to 
p2m_create_table().

>The error you describe in your mail is usually happening in the early setup.
That seems to be the case, yes. I haven't been able to see anything that's 
happening in the VM before this.

>I don't think this is the bug, as said above we don't map anything to address 
>0 and this is normal because it's not part of the layout.
Ok. It certainly wouldn't be surprising if I'm getting my address types mixed 
up :-) 

>It would be useful if you provide the version of Xen and Linux you use.
Xen is a recent git clone - cb34a7c8d741, with a couple of small hacks that we 
needed to get to the point of Dom0 running on our platform (there's a change to 
xen/drivers/char/ns16550.c to workaround a uart bug, and one to 
xen/arch/platforms/brcm.c to set dom0_gnttab_start and dom0_gnttab_end).
Linux Kernel is 3.14. I took our kernel, enabled the various CONFIG options for 
Xen and rebuilt it.

Thanks,

Chris


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