Hi Bhupesh, Sorry for top posting. Because I don't know which line at below I should add comment into. So could you plese tell what problem you have met in user space tools? Which user space tool is broken so that we need export page_offset_base to vmcoreinfo? Sorry I didn't get what problem this patch is trying to fix from the patch log. About this, I have replied to you in lkml.kernel.org/r/20181025063446.GD2120@MiWiFi-R3L-srv You might miss it. About this exporting, I ever posted patch to upstream and we have had discussion, please check https://lore.kernel.org/patchwork/patch/723472/ In makedumpfile and crash, we have had a clear method to analyze and deduce it from kcore or vmcore. Thanks Baoquan On 10/27/18 at 04:13am, Bhupesh Sharma wrote: > Since commit 23c85094fe1895caefdd > ["proc/kcore: add vmcoreinfo note to /proc/kcore"]), '/proc/kcore' > contains a new PT_NOTE which carries the VMCOREINFO information. > > If the same is available, one can use it in user-land to > retrieve machine specific symbols or strings being appended to the > vmcoreinfo even for live-debugging of the primary kernel as a > standard interface exposed by kernel for sharing machine specific > details with the user-land. > > In the past I had a discussion with James, where he suggested this > approach (please see [0]) and I really liked the idea. Since then I > have been working on unifying the implementations of > (atleast) the commonly used user-space utilities that provide > live-debugging capabilities (tools like 'makedumpfile' and > 'crash-utility', see [1] for details of these tools). > > For the same, when live debugging on x86_64 machines, user-space > tools currently rely on different mechanisms to determine > the 'page_offset_base' value (i.e. start of direct mapping of all > physical memory). One of the approach used by 'makedumpfile' > user-space tool for e.g. is to calculate the same from the last > PT_LOAD available in '/proc/kcore', which can be flaky as and when > new sections (for e.g. KCORE_REMAP which was added > to recent kernels) are added to kcore. > > For other architectures like arm64, I have already proposed using > the vmcoreinfo note (in '/proc/kcore') in the user-space utilities to > determine machine specific details like VA_BITS, PAGE_OFFSET, > kasrl_offset() (see [2] for details), for which different user-space > tools earlier used different (and at times flaky) approaches like: > > - Reading kernel CONFIGs from user-space and determining CONFIG values > like VA_BITS from there. > - Reading symbols from '/proc/kallsyms' and determining their values > via '/dev/mem' interface. > - Reading symbols from 'vmlinux' and determing their values from > reading memory. > > This patch allows appending 'page_offset_base' for x86_64 platforms > to vmcoreinfo, so that user-space tools can use the same as a standard > interface to determine the start of direct mapping of all physical > memory. > > Testing: > ------- > - I tested this patch (rebased on 'linux-next') on a x86_64 machine > using the modified 'makedumpfile' user-space code (see [3] for my > github tree which contains the same) for determining how many pages > are dumpable when different dump_level is specified (which is > one use-case of live-debugging via 'makedumpfile'). > - I tested both the KASLR and non-KASLR boot cases with this patch. > - Here is one sample log (for KASLR boot case) on my x86_64 machine: > > < snip..> > The kernel doesn't support mmap(),read() will be used instead. > > TYPE PAGES EXCLUDABLE DESCRIPTION > ---------------------------------------------------------------------- > ZERO 21299 yes Pages filled > with zero > NON_PRI_CACHE 91785 yes Cache > pages without private flag > PRI_CACHE 1 yes Cache pages with > private flag > USER 14057 yes User process > pages > FREE 740346 yes Free pages > KERN_DATA 58152 no Dumpable kernel > data > > page size: 4096 > Total pages on system: 925640 > Total size on system: 3791421440 Byte > > I understand that there might be some reservations about exporting > such machine-specific details in the vmcoreinfo, but to unify > the implementations across user-land and archs, perhaps this would be > good starting point to start a discussion. > > [0]. https://www.mail-archive.com/kexec@xxxxxxxxxxxxxxxxxxx/msg20300.html > [1]. MAN pages -> MAKEDUMPFILE(8) and CRASH(8) > [2]. https://www.spinics.net/lists/kexec/msg21608.html > http://lists.infradead.org/pipermail/kexec/2018-October/021725.html > [3]. https://github.com/bhupesh-sharma/makedumpfile/tree/add-page-offset-base-to-vmcore-v1 > > Cc: Boris Petkov <bp@xxxxxxxxx> > Cc: Baoquan He <bhe@xxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx> > Cc: Dave Anderson <anderson@xxxxxxxxxx> > Cc: James Morse <james.morse@xxxxxxx> > Cc: Omar Sandoval <osandov@xxxxxx> > Cc: x86@xxxxxxxxxx > Cc: kexec@xxxxxxxxxxxxxxxxxxx > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Signed-off-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx> > --- > arch/x86/kernel/machine_kexec_64.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c > index 4c8acdfdc5a7..834ccefef867 100644 > --- a/arch/x86/kernel/machine_kexec_64.c > +++ b/arch/x86/kernel/machine_kexec_64.c > @@ -356,6 +356,7 @@ void arch_crash_save_vmcoreinfo(void) > VMCOREINFO_SYMBOL(init_top_pgt); > vmcoreinfo_append_str("NUMBER(pgtable_l5_enabled)=%d\n", > pgtable_l5_enabled()); > + VMCOREINFO_NUMBER(page_offset_base); > > #ifdef CONFIG_NUMA > VMCOREINFO_SYMBOL(node_data); > -- > 2.7.4 > _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
