[CRIU] VM_IO or VM_PFNMAP mappings

[Sowmini Varadhan]

On (10/27/14 16:04), Cyrill Gorcunov wrote:
> > > 
> > > Turns out these come up as a result of vdso
> > > [http://stackoverflow.com/questions/19938324/what-are-vdso-and-vsyscall]. 
> > > The stack trace is:
> > > 
> > >  [  123.107756]  [<ffffffff81196395>] remap_pfn_range+0xa5/0x480
> > >  [  123.107763]  [<ffffffff8106678b>] map_vdso+0x1ab/0x240
> > >  [  123.107769]  [<ffffffff810668ce>] compat_arch_setup_additional_pages+0x7e/0xc0
> > >  [  123.107774]  [<ffffffff81232a31>] load_elf_binary+0xac1/0x1830
> > >  [  123.107781]  [<ffffffff811e1587>] search_binary_handler+0x97/0x1d0
> > >  [  123.107787]  [<ffffffff811e29d1>] do_execve_common.isra.24+0x481/0x610
> > >  [  123.107794]  [<ffffffff811e2da9>] SyS_execve+0x29/0x30
> > >  [  123.107800]  [<ffffffff81765c09>] stub_execve+0x69/0xa0
> > 
> > Cyrill, do you know anything about VDSO remapping?
> 
> It would be great to know the background of this conversation, what the
> problem was in the first place?

I was trying out live-migrationof a connected iperf server process
using  criu (without p.haul helpers) from first-principles, but 
criu was failing with 

> > Error (proc_parse.c:357): Unsupported mapping found 00000000f7786000-00000000f7788000
> > Error (bfd.c:118): Error flushing image

Investigation of /proc/$pid/smaps showed "pf" and "io" VmFlags 
were triggering this. and investigation of the cause of those flags
resulted in the above.

> As to stack backtrace -- this is standart setup of a new memory map
> for Elf executable. The new vDSO format (well, relatively new, since 3.16)
> implies presence of vvar zone which has  VM_IO | VM_PFNMAP flags, this
> area prepared to the process by the kernel. So guys, could you please
> describe what the problem we're trying to solve here.
> 

http://lists.openvz.org/pipermail/criu/2014-October/017590.html