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

On 24/11/15 13:39, Jan Beulich wrote: >>>> 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. The idle_pg_table is already present in the VMCORE notes.