On Mon, 29 Jul 2013 16:37:12 +0200 Laszlo Ersek <ler...@redhat.com> wrote:
> (Apologies for the long To: list, I'm including everyone who > participated in > <https://lists.gnu.org/archive/html/qemu-devel/2012-09/msg02607.html>). > > Conceptually, the dump-guest-memory command works as follows: > (a) pause the guest, > (b) get a snapshot of the guest's physical memory map, as provided by > qemu, > (c) retrieve the guest's virtual mappings, as seen by the guest (this is > where paging=true vs. paging=false makes a difference), > (d) filter (c) as requested by the QMP caller, > (e) write ELF headers, keying off (b) -- the guest's physmap -- and (d) > -- the filtered guest mappings. > (f) dump RAM contents, keying off the same (b) and (d), > (g) unpause the guest (if necessary). > > Patch #1 affects step (e); specifically, how (d) is matched against (b), > when "paging" is "true", and the guest kernel maps more guest-physical > RAM than it actually has. > > This can be done by non-malicious, clean-state guests (eg. a pristine > RHEL-6.4 guest), and may cause libbfd errors due to PT_LOAD entries > (coming directly from the guest page tables) exceeding the vmcore file's > size. > > Patches #2 to #4 are independent of the "paging" option (or, more > precisely, affect them equally); they affect (b). Currently input > parameter (b), that is, the guest's physical memory map as provided by > qemu, is implicitly represented by "ram_list.blocks". As a result, steps > and outputs dependent on (b) will refer to qemu-internal offsets. > > Unfortunately, this breaks when the guest-visible physical addresses > diverge from the qemu-internal, RAMBlock based representation. This can > happen eg. for guests > 3.5 GB, due to the 32-bit PCI hole; see patch #4 > for a diagram. > > Patch #2 introduces input parameter (b) explicitly, as a reasonably > minimal map of guest-physical address ranges. (Minimality is not a hard > requirement here, it just decreases the number of PT_LOAD entries > written to the vmcore header.) Patch #3 populates this map. Patch #4 > rebases the dump-guest-memory command to it, so that steps (e) and (f) > work with guest-phys addresses. > > As a result, the "crash" utility can parse vmcores dumped for big x86_64 > guests (paging=false). Applied to the qmp branch, thanks. > > Please refer to Red Hat Bugzilla 981582 > <https://bugzilla.redhat.com/show_bug.cgi?id=981582>. > > Disclaimer: as you can tell from my progress in the RHBZ, I'm new to the > memory API. The way I'm using it might be retarded. > > Laszlo Ersek (4): > dump: clamp guest-provided mapping lengths to ramblock sizes > dump: introduce GuestPhysBlockList > dump: populate guest_phys_blocks > dump: rebase from host-private RAMBlock offsets to guest-physical > addresses > > include/sysemu/dump.h | 4 +- > include/sysemu/memory_mapping.h | 30 ++++++- > dump.c | 171 +++++++++++++++++++++----------------- > memory_mapping.c | 174 > +++++++++++++++++++++++++++++++++++++-- > stubs/dump.c | 3 +- > target-i386/arch_dump.c | 10 ++- > 6 files changed, 300 insertions(+), 92 deletions(-) >
