Re: [Crash-utility] [Xen-devel] crash tool - problem with new Xen linear virtual mapped sparse p2m list

>> On 24.11.15 at 13:57, <ptesarik(a)suse.cz&gt; wrote: V Tue, 24 Nov 2015 10:35:03 +0000 Andrew Cooper <andrew.cooper3(a)citrix.com&gt; napsáno: > On 24/11/15 10:17, Petr Tesarik wrote: > > On Tue, 24 Nov 2015 10:09:01 +0000 > > David Vrabel <david.vrabel(a)citrix.com&gt; wrote: > > > >> On 24/11/15 09:55, Malcolm Crossley wrote: > >>> On 24/11/15 08:59, Jan Beulich wrote: > >>>>>>> On 24.11.15 at 07:55, <JGross(a)suse.com&gt; wrote: > >>>>> What about: > >>>>> > >>>>> 4) Instead of relying on the kernel maintained p2m list for m2p > >>>>> conversion use the hypervisor maintained m2p list which should be > >>>>> available in the dump as well. This is the way the alive kernel is > >>>>> working, so mimic it during crash dump analysis. > >>>> I fully agree; I have to admit that looking at the p2m when doing page > >>>> table walks for a PV Dom0 (having all machine addresses in page table > >>>> entries) seems kind of backwards. (But I say this knowing nothing > >>>> about the tool.) > >>>> > >>> I don't think we can reliably use the m2p for PV domains because > >>> PV domains don't always issue a m2p update hypercall when they change > >>> their p2m mapping. > >> This only applies to foreign pages which won't be very interesting to a > >> crash tool. > > True. I think the main reason crash hasn't done this is that it cannot > > find the hypervisor maintained m2p list. It should be sufficient to add > > some more fields to XEN_VMCOREINFO, so that crash can locate the > > mapping in the dump. > > The M2P lives at an ABI-specified location in all virtual address spaces > for PV guests. > > Either 0xF5800000 or 0xFFFF800000000000 depending on bitness. Hm, this is nice, but kind of chicken-and-egg problem. A system dump contains a snapshot of the machine's RAM. But the addresses you mentioned are virtual addresses. How do I translate them to physical addresses without an m2p mapping? I need at least the value of CR3 for that domain, and most likely a way to determine if it is a PV domain.