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

>> On 24.11.15 at 14:46, <ian.campbell(a)citrix.com&gt; wrote: On Tue, 2015-11-24 at 10:35 +0000, Andrew Cooper wrote: > 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. In theory it can actually be dynamic. XENMEM_machphys_mapping is the way to get at it (for both bitnesses). For 64-bit guests I think that is most an "in theory" thing and it never has actually been so. For a 32-bit guest case I don't recall if it is just a 32on32 vs 32on64 thing, or if something (either guest or toolstack) gets to pick more dynamically or even if it is a dom0 vs domU thing.