On Fri, Aug 05, 2016 at 11:26:47AM +0200, Andrew Jones wrote: > On Thu, Aug 04, 2016 at 10:41:16AM +0200, Laurent Vivier wrote: > > > > > > On 04/08/2016 04:38, David Gibson wrote: > > > On Wed, Aug 03, 2016 at 09:55:07PM +0200, Laurent Vivier wrote: > > >> If we don't provide the page size in target-ppc:cpu_get_dump_info(), > > >> the default one (TARGET_PAGE_SIZE, 4KB) is used to create > > >> the compressed dump. It works fine with Macintosh, but not with > > >> pseries as the kernel default page size is 64KB. > > >> > > >> Without this patch, if we generate a compressed dump in the QEMU monitor: > > >> > > >> (qemu) dump-guest-memory -z qemu.dump > > >> > > >> This dump cannot be read by crash: > > >> > > >> # crash vmlinux qemu.dump > > >> ... > > >> WARNING: cannot translate vmemmap kernel virtual addresses: > > >> commands requiring page structure contents will fail > > >> ... > > >> > > >> Signed-off-by: Laurent Vivier <lviv...@redhat.com> > > >> --- > > >> target-ppc/arch_dump.c | 5 +++++ > > >> 1 file changed, 5 insertions(+) > > > > > > Urgh.. so, really the page size used by the guest kernel is a > > > guest-side detail, and it's certainly possible to build a 4kiB page > > > guest kernel, although 64kiB is the norm. > > > > virtio-balloon doesn't work with 4K kernel. > > > > > This might be the best we can do, but it'd be nice if we could probe > > > or otherwise avoid relying on this assumption about the guest kernel. > > > > I agree with you but none of the other architectures probes for the page > > size. > > > > For instance ARM: |I cc: Drew to know how he has chosen the values] > > > > if (arm_feature(env, ARM_FEATURE_AARCH64)) { > > ... > > info->page_size = (1 << 16); > > ... > > } else { > > ... > > info->page_size = (1 << 12); > > ... > > } > > > > info->page_size is used to determine the dumpfile's block size. The > block size needs to be at least the page size, but a multiple of page > size works fine too. As we can't probe for the currently used guest > page size, and a multiple of page size is fine, then using the guest's > maximum allowed page size is the best we can do.
Aha! Well that makes life much easier. I'll adjust the commit message and apply. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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