Re: [Crash-utility] [PATCH] Do not create arch-specific p2m mapping for ELF xen dumps

On Fri, 18 Dec 2015 09:33:55 -0500 (EST) Dave Anderson <anderson(a)redhat.com&gt; wrote: > ----- Original Message ----- > > Hello Dave, > > > > Let me send you a cleanup/fix for Xen DomU dumps. > > > > When opening a Xen DomU dump without auto-translated addresses (e.g. > > from an x86_64 PV domain), a mapping between physical and machine > > pages is needed. An xc_core dump file does not contain this mapping, > > so it must be created by arch-specific code from the dumped data. > > > > This (and only this) is the job of the machdep->xendump_p2m_create > > callback, which is called if the XC_CORE_P2M_CREATE flag is set. ELF > > files contain the mapping in a separate section (".xen_p2m"), so this > > arch-specific code is not needed and should not be run. > > > > On the other hand, XC_CORE_P2M_CREATE also triggers the initialization > > of the elf_index_pfn array. I believe this should be in fact controlled > > by XC_CORE_PFN_CREATE, because the flag is not used for anything else. > > > > I found this issue thanks to a Xen DomU ELF dump file that contained an > > invalid CR3 value, which could not be used to translate kvaddr to maddr. > > Without the patch, session initialization fails with these messages: > > > > crash: cannot find mfn 0 (0x0) in page index > > > > crash: cannot read/find pud page > > > > Signed-off-by: Petr Tesarik <ptesarik(a)suse.com&gt; > > > > Hi Petr, > > This looks good. Can you help me come up with a succinct blurb > for the changelog? > > From my test output, it's now obvious that the gathering of the > p2m_frames/p2m_frame_index_list is unnecessary in the case of PV > kernel dumps (correct?). Not quite. It is still necessary for xc_core files. It is not necessary for ELF format files. > And you ran into a situation in which an > invalid CR3 in the header caused the (unnecessary) p2m frame-gathering > to fail, and as a result the crash session itself was aborted. This part is perfect. Petr T