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

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.