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

[Oren Laadan]

Serge E. Hallyn wrote:
> 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().

Interesting, I didn't think about it.

So yes, switching temporarily should work. An alternative we can
do the call destroy_mm() earlier, as it may suit us.

> 
>> 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?
> 

Couldn't you use the same machine you are using - just reboot it
between checkpoint and restart with a 32bit kernel ... ?

Oren.
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