Re: [Xen-devel] BUG: bad page map under Xen

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.10.13 at 16:44, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> On Mon, Oct 21, 2013 at 03:27:50PM +0100, Jan Beulich wrote:
>> >>> On 21.10.13 at 16:18, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
>> >>> wrote:
>> > On Mon, Oct 21, 2013 at 04:06:07PM +0200, Lukas Hejtmanek wrote:
>> >>         Region 2: Memory at 380fff000000 (64-bit, prefetchable) [size=8M]
>> >...
>> > --- a/arch/x86/xen/setup.c
>> > +++ b/arch/x86/xen/setup.c
>> > @@ -92,6 +92,9 @@ static void __init xen_add_extra_mem(u64 start, u64 size)
>> >  
>> >                 __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
>> >         }
>> > +       /* Anything past the balloon area is marked as identity. */
>> > +       for (pfn = xen_max_p2m_pfn; pfn < MAX_DOMAIN_PAGES; pfn++)
>> > +               __set_phys_to_machine(pfn, IDENTITY_FRAME(pfn));
>> 
>> Hardly - MAX_DOMAIN_PAGES derives from
>> CONFIG_XEN_MAX_DOMAIN_MEMORY, which in turn is unrelated
>> to where MMIO might be. Should you perhaps simply start from
> 
> Looks like your mailer ate some words.

I don't think so - they're all there in the text you quoted.

>> an all 1:1 mapping, inserting the RAM translations as you find
>> them?
> 
> 
> Yeah, as this code can be called for the regions under 4GB. Definitly
> needs more analysis.
> 
> Were you suggesting a lookup when we scan the PCI devices? (xen_add_device)?

That was for PVH, and is obviously fragile, as there can be MMIO
regions not matched by any PCI device's BAR. We could hope for
all of them to be below 4Gb, but I think (based on logs I got to see
recently from a certain vendor's upcoming systems) this isn't going
to work out.

Jan


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