Re: [Crash-utility] [PATCH] xen: Add support for domU with Linux kernel 3.19 and newer

----- Original Message ----- > crash patch c3413456599161cabc4e910a0ae91dfe5eec3c21 (xen: Add support for > dom0 with Linux kernel 3.19 and newer) from Daniel made crash utility > support xen dom0 vmcores after linux kernel commit > 054954eb051f35e74b75a566a96fe756015352c8 (xen: switch to linear virtual > mapped sparse p2m list). > > This patch can be deemed as a subsequent and make this utility support Xen > PV domU dumpfiles again. > > Basically speaking, readmem() can't be used to read xen_p2m_addr associate > memory directly during m2p translation. It introduces infinite recursion. > Following call sequence shows the scenario, it comes from a section of > backtrace with only kvaddr, machine addr and mfn left as parameter: > > module_init() > > /* The first readmem() from module_init(). */ > readmem(addr=0xffffffffa02fe4a0) > > /* readmem() needs physical address, so calls kvtop(). */ > kvtop(kvaddr=0xffffffffa02fe4a0) > x86_64_kvtop(kvaddr=ffffffffa02fe4a0) > > /* Calculate physical address by traversing page tables. */ > x86_64_kvtop_xen_wpt(kvaddr=0xffffffffa02fe4a0) > > /* > * x86_64_kvtop_xen_wpt() is going to traverse the page table to > * get the physical address for 0xffffffffa02fe4a0. So, at first it > * is needed to translate the pgd from machine address to physical > * address. So invoke xen_m2p() here to do the translation. 0x58687f000 > * is the pgd machine address in x86_64_kvtop_xen_wpt() and is needed > * to be translated to its physical address. > */ > xen_m2p(machine=0x58687f000) > __xen_m2p(machine=0x58687f000, mfn=0x58687f) > > /* > * __xen_m2p() is going to search mfn 0x58687f in p2m VMA which starts > * at VMA 0xffffc900001cf000. It compares every mfn stored in it with > * 0x58687f. Once it's proved 0x58687f is one mfn in the p2m, its offset > * will be used to calculate the pfn. > * > * readmem() is invoked by __xen_m2p() to read the page from VMA > * 0xffffc900001cf000 here. > */ > readmem(addr=0xffffc900001cf000) > > /* > * readmem() needs physical address of 0xffffc900001cf000 to make the > * reading done. So it invokes kvtop() to get the physical address. > */ > kvtop(kvaddr=0xffffc900001cf000) > x86_64_kvtop(kvaddr=0xffffc900001cf000) > > /* It needs to calculate physical address by traversing page tables. */ > x86_64_kvtop_xen_wpt(kvaddr=0xffffc900001cf000) > > /* > * 0x581b7e000 is the machine address of pgd need to be translated here. > * The mfn is calculated in this way at x86_64_kvtop_xen_wpt(): > * > * pml4 = ((ulong *)machdep->machspec->pml4) + pml4_index(kvaddr); > * pgd_paddr = (*pml4) & PHYSICAL_PAGE_MASK; > * > * The kvaddr 0xffffc900001cf000 here is quite different from the one > * above, so the machine address of pgd is not the same one. And this > * pgd is the one we use to access the VMA of p2m table. > */ > xen_m2p(machine=0x581b7e000) > __xen_m2p(machine=0x581b7e000, mfn=0x581b7e) > > /* > * Looking for mfn 0x581b7e in the range of p2m page which starts at > * VMA 0xffffc900001f5000. > */ > readmem(addr=0xffffc900001f5000) > > /* Need physical address of VMA 0xffffc900001f5000 as same reason above. */ > kvtop(kvaddr=0xffffc900001f5000) > x86_64_kvtop(kvaddr=0xffffc900001f5000) > > /* Need to traverse page tables to calculate physical address for it. */ > x86_64_kvtop_xen_wpt(kvaddr=0xffffc900001f5000) > > /* > * Unfortunately, machine address 0x581b7e000 have to be translated again. > * Endless loop starts from here. > */ > xen_m2p(machine=0x581b7e000) > __xen_m2p(machine=0x581b7e000, mfn=0x581b7e) > readmem(addr=0xffffc900001f5000) > > Fortunately, PV domU p2m mapping is also stored at xd->xfd + xch_index_offset > and organized as struct xen_dumpcore_p2m. We have a chance to read the p2m > stuff directly from there, and then we avoid the loop above. > > So, this patch implements a special reading function read_xc_p2m() to extract > the mfns from xd->xfd + xch_index_offset. This function does not need to read > mfns from p2m VMA like readmem() does, so, we avoid the endless loop introduced > by the address translation. > > Signed-off-by: Honglei Wang <honglei.wang(a)oracle.com&gt; > Reviewed-by: Daniel Kiper <daniel.kiper(a)oracle.com&gt; Queued for crash-7.2.0: https://github.com/crash-utility/crash/commit/5c52842a58a2602dba81de71831...