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. This ought to also be present in Xen's master page table (idle_pg_table[]), and I suppose we can take for granted a symbol table being available.