Re: Nouveau on dom0

[Arvind R <arvino55@gmail.com>]

On Wed, Mar 3, 2010 at 11:43 PM, Konrad Rzeszutek Wilk
<konrad.wilk@oracle.com> wrote:
>> > aio-write -
>>
>> which triggers do_page_fault, handle_mm_fault, do_linear_fault, __do_fault
>> and finally ttm_bo_vm_fault.

> I've attached a simple patch I wrote some time ago to get the real MFNs
> and its page protection. I think you can adapt it (print_data function to be exact)
> to peet at the PTE and its protection values.
Have patched - did not apply clean. Will compile and get some info.

> There is an extra flag that the PTE can have when running under Xen: _PAGE_IOMAP.
> This signifies that the PFN is actually the MFN. In this case thought
> it sholdn't be enabled b/c the memory is actually gathered from
> alloc_page. But if it is, it might be the culprit.

>> What can possibly cause the fault-handler to repeat endlessly?

FYI: about 2000 times a second - slowed by printk

>> If a wrong page is backed at the user-address, it should create bad_access or
>> some other subsequent events - but the system is running fine minus all local
> So  you see this fault handler being called endlessly while the machine
> is still running and other pieces of code work just fine, right?
Right. Can ssh in - but no local console

>> ttm_tt_get_page calls alloc in a loop - so it may allocate multiple pages from
>> start/end depending on Highmem memory or not - implying asynchronous allocation
>> and mapping.
>
> I thought it had some logic to figure out that it already handled this
> page and would return an already allocate page?
Right.

I think the problem lies in the vm_insert_pfn/page/mixed family of functions.
These are only used (grep'ed kernel tree) and invariably for mmaping.
Scsi-tgt, mspec, some media/video, poch,android in staging and ttm
- and, surprise - xen/blktap/ring.c and device.c
- which both check XENFEAT_auto_translated_physmap

Pls. look at xen/blktap/ring.c - it looks to be what we need