[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] crash tool - problem with new Xen linear virtual mapped sparse p2m list
On 24/11/15 13:41, Andrew Cooper wrote: > On 24/11/15 13:39, Jan Beulich wrote: >>>>> On 24.11.15 at 13:57, <ptesarik@xxxxxxx> wrote: >>> V Tue, 24 Nov 2015 10:35:03 +0000 >>> Andrew Cooper <andrew.cooper3@xxxxxxxxxx> napsÃno: >>> >>>> On 24/11/15 10:17, Petr Tesarik wrote: >>>>> On Tue, 24 Nov 2015 10:09:01 +0000 >>>>> David Vrabel <david.vrabel@xxxxxxxxxx> 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@xxxxxxxx> 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. Ah, except it is aliased to the name pgd_l4. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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