Re: [Xen-devel] [PATCH 0 of 5] update xenctx to dump pagetables

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 22.06.11 at 15:50, Olaf Hering <olaf@xxxxxxxxx> wrote:
> On Tue, Jun 21, Jan Beulich wrote:
> 
>> >>> On 21.06.11 at 11:59, Tim Deegan <Tim.Deegan@xxxxxxxxxx> wrote:
>> > Hi, 
>> > 
>> > At 17:56 -0400 on 20 Jun (1308592583), Konrad Rzeszutek Wilk wrote:
>> >> > Any ideas why some mfns are not accessible?
>> >> 
>> >> They look to be the special I/O PFNs. The ones that cover ACPI, 
> framebuffer,
>> >> PCI IO bars, MP tale.
>> > 
>> > I think they're too high for that, but if you can post the e820 map of
>> > the system this happened on then we'll know. 
>> > 
>> >> > Are there any other paging states maintained outside of the guests
>> >> > memory?
>> >> 
>> >> They look to be I/O pages.
>> >> 
>> >> But not sure why they are mapped to your guest?
>> > 
>> > But they're not mapped into the guest - from the look of them they're
>> > not mapped anywhere.  You could add some extra printouts around that
>> > warning in mm.c to show whether the MFNs are valid and if so which
>> > domain owns them.
>> > 
>> > Also, interesting that it's the addresses just above 0xffff800000000000
>> > that are different - what lives at that address in the PV kernel you're
>> > running?
>> 
>> That's Xen's space, isn't it. Clearly any non-hypervisor based page
>> table walking code has to ignore this range for PV guests' page
>> tables.
> 
> Is there a way to detect that? I cant seem to match any of these ranges to
> something in guests dmesg or /proc.

No need for detection - the hole is part of the ABI (minus its dynamic
size in 32-bit pv guests running on 64-bit hypervisor - that may require
use of heuristics).

Jan


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