[Devel] Re: [PATCH 1/1] fill vdso with syscall32_setup_pages if TIF_IA32 on x86_64

[Serge E. Hallyn]

Quoting Oren Laadan (orenl at cs.columbia.edu):
> 
> Cool !
> 
> So what do we have working now for 64 bit kernel (for 32 bit kernel
> we know it works...):
> 
> 	'restart'	checkpointed
> 	 program	  program
> 	----------------------------------------
> 	  64bit		  64bit		-> works
> 	  32bit		  32bit		-> works
> 
> 	  64bit		  32bit		-> ?????

Actually the other way around works - /bin/restart_32 < 64bit.out
works just fine.  /bin/restart_64 < 32bit.out does not.  The reason
is that destroy_mm() ends up calling do_munmap on a 64-bit mapping
after the switch to 32-bit had been made, and it refuses bc
vma->vm_start > TASK_SIZE.

Perhaps getting it to work will be as simple as temporarily switching
back to 64-bit during destroy_mm().

> Does it make sense to allow the opposite transition: 'restart' starts
> as a 32bit and becomes a 64bit after it restores the state from the
> image ?
> 
> And what about if you checkpoint on a 32 bit kernel and try to 
> restart on a 64 bit kernel, and vice versa ?  (in both cases, the
> program of course is 32bit, and we can assume same physical host
> for now). 

I have no hw right now where I could test such a thing.  Do you?
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