Re: [Xen-devel] [PATCH] kexec-tools: Read always one vmcoreinfo file

[Petr Tesarik <ptesarik@xxxxxxx>]

On Thu, 13 Nov 2014 18:22:17 +0100
Daniel Kiper <daniel.kiper@xxxxxxxxxx> wrote:

> Hi Petr,
> 
> On Thu, Nov 13, 2014 at 04:51:48PM +0100, Petr Tesarik wrote:
> > Hi all,
> >
> > this thread got somehow forgotten because of vacations...
> > Anyway, read below.
> >
> > On Tue, 24 Jul 2012 15:54:10 +0200
> > Daniel Kiper <daniel.kiper@xxxxxxxxxx> wrote:
> >
> > > On Tue, Jul 24, 2012 at 10:18:34AM +0200, Petr Tesarik wrote:
> > > > Dne Po 23. ??ervence 2012 22:10:59 Daniel Kiper napsal(a):
> > > > > Hi Petr,
> > > > >
> > > > > On Mon, Jul 23, 2012 at 03:30:55PM +0200, Petr Tesarik wrote:
> > > > > > Dne Po 23. ??ervence 2012 14:56:07 Petr Tesarik napsal(a):
> > > > > > > Dne ??t 5. ??ervence 2012 14:16:35 Daniel Kiper napsal(a):
> > > > > > > > vmcoreinfo file could exists under /sys/kernel (valid on 
> > > > > > > > baremetal
> > > > > > > > only) and/or under /sys/hypervisor (valid when Xen dom0 is 
> > > > > > > > running).
> > > > > > > > Read only one of them. It means that only one PT_NOTE will be 
> > > > > > > > always
> > > > > > > > created. Remove extra code for second PT_NOTE creation.
> > > > > > >
> > > > > > > Hi Daniel,
> > > > > > >
> > > > > > > are you absolutely sure this is the right thing to do? IIUC these 
> > > > > > > two
> > > > > > > VMCORINFO notes are very different. The one from 
> > > > > > > /sys/kernel/vmcoreinfo
> > > > > > > describes the Dom0 kernel (type 'VMCOREINFO'), while the one from
> > > > > > > /sys/hypervisor describes the Xen hypervisor (type 
> > > > > > > 'XEN_VMCOREINFO').
> > > > > > > If you keep only the hypervisor note, then e.g. makedumpfile 
> > > > > > > won't be
> > > > > > > able to use dumplevel greater than 1, nor will it be able to 
> > > > > > > extract
> > > > > > > the log buffer.
> > > > > >
> > > > > > I've just verified this, and I'm confident we have to keep both 
> > > > > > notes in
> > > > > > the dump file. Simon, please revert Daniel's patch to avoid 
> > > > > > regressions.
> > > > > >
> > > > > > I'm attaching a sample VMCOREINFO_XEN and VMCOREINFO to demonstrate 
> > > > > > the
> > > > > > difference. Note that the VMCOREINFO_XEN note is actually too big,
> > > > > > because Xen doesn't bother to maintain the correct note size in the 
> > > > > > note
> > > > > > header, so it always spans a complete page minus 
> > > > > > sizeof(Elf64_Nhdr)...
> > > > >
> > > > > [...]
> > > > >
> > > > > The problem with /sys/kernel/vmcoreinfo under Xen is that it expose 
> > > > > invalid
> > > > > physical address. It breaks /proc/vmcore in crash kernel. That is why 
> > > > > I
> > > > > proposed that fix. Additionally, /sys/kernel/vmcoreinfo is not 
> > > > > available
> > > > > under Xen Linux Ver. 2.6.18. However, I did not do any makedumpfile 
> > > > > tests.
> > > > > If you discovered any issues with my patch please drop me more details
> > > > > about your tests (Xen version, Linux Kernel version, makedumpfile 
> > > > > version,
> > > > > command lines, config files, logs, etc.). I will be more then happy to
> > > > > fix/improve kexec-tools and makedumpfile.
> > > >
> > > > Hi Daniel,
> > > >
> > > > well, Linux v2.6.18 does not have /sys/kernel/vmcoreinfo, simply 
> > > > because the
> > > > VMCOREINFO infrastructure was not present in 2.6.18. It was added later 
> > > > with
> > >
> > > Yep.
> > >
> > > > commit fd59d231f81cb02870b9cf15f456a897f3669b4e, which went into 2.6.24.
> > >
> > > Hmmm... As I know 2.6.24 does not support kexec/kdump under Xen dom0. 
> > > Correct?
> > >
> > > > I tested with the following combinations:
> > > >
> > > > * xen-3.3.1 + kernel-xen-2.6.27.54 + kexec-tools-2.0.0 + 
> > > > makedumpfile-1.3.1
> > > > * xen-4.0.3 + kernel-xen-2.6.32.59 + kexec-tools-2.0.0 + 
> > > > makedumpfile-1.3.1
> > > > * xen-4.1.2 + kernel-xen-3.0.34 + kexec-tools-2.0.0 + makedumpfile-1.4.0
> > > >
> > > > These versions correspond to SLES11-GA, SLES11-SP1 and SLES11-SP2,
> > > > respectively. All of them work just fine and save both ELF notes into 
> > > > the
> > > > dump.
> > >
> > > Could you test current kexec-tools development version and
> > > latest makedumpfile version on latest SLES version?
> >
> > And indeed, I've just hit this regression with SLES12 GA (kernel 3.12.28,
> > kexec-tools 2.0.5, makedumpfile 1.5.6).
> >
> > In the secondary kernel, makedumpfile complains that VMCOREINFO is not
> > stored in /proc/vmcore:
> >
> > bash-4.2# makedumpfile -d 31 -X -E /proc/vmcore 
> > /kdump/mnt1/abuild/dumps/2014-11-13-13\:13/vmcore.elf
> > Switched running mode from cyclic to non-cyclic,
> > because the cyclic mode doesn't support Xen.
> > /proc/vmcore doesn't contain vmcoreinfo.
> > Specify '-x' option or '-i' option.
> > Commandline parameter is invalid.
> > Try `makedumpfile --help' for more information.
> >
> > makedumpfile Failed.
> >
> > Then I reverted commit 455d79f57e9367e5c59093fd74798905bd5762fc and
> > everything works just fine.
> >
> > > > What do you mean by "invalid physical address"? I'm getting the correct
> > > > physical address under Xen. Obviously, it must be translated to machine
> > > > addresses if you need them from the secondary kernel.
> > >
> > > Correct vmcoreinfo address should be established by calling
> > > HYPERVISOR_kexec_op(KEXEC_CMD_kexec_get_range, KEXEC_RANGE_MA_VMCOREINFO).
> >
> > The addresses I get from /sys/kernel/vmcoreinfo and
> > from /sys/hypervisor/vmcoreinfo are machine addresses in both cases, so
> > when a non-Xen kernel is used for dumping, everything works as expected.
> >
> > I am well aware that the Xen implementation in SLES differs
> > substantially from mainline, but it seems to me that:
> >
> >   1. both VMCOREINFO and VMCOREINFO_XEN is required for dumpfile
> >      filtering, and
> >   2. both sysfs files should report machine addresses, because the current
> >      p2m mapping is lost forever when the hypervisor executes the secondary
> >      kernel, so physical addresses are pretty useless.
> >
> > I'm reverting the patch for the SLES distro, but I'd like to reach some
> > kind of consensus with the community, too.
> 
> This reminds me something. I saw that kind of thing when I was working on
> makedumpfile once. I have this issue on my TODO list. However, currently
> I am working on EFI and multiboot2 stuff and I am not able to take a
> look at it. I will do that after releasing first version of patches.
> Probably in the middle of December. Is it OK for you?

Since this issue has waited two years now, I think it can also wait
another month or two. ;-)

Thanks,
Petr T

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