Le 01/05/2019 à 12:32, Michael Ellerman a écrit :
> Laurent Dufour <ldufour@linux.vnet.ibm.com> writes:
>> Le 23/04/2019 à 18:04, Dave Hansen a écrit :
>>> On 4/23/19 4:16 AM, Laurent Dufour wrote:
> ...
>>>> There are 2 assumptions here:
>>>>    1. 'start' and 'end' are page aligned (this is guaranteed by __do_munmap().
>>>>    2. the VDSO is 1 page (this is guaranteed by the union vdso_data_store on powerpc)
>>>
>>> Are you sure about #2?  The 'vdso64_pages' variable seems rather
>>> unnecessary if the VDSO is only 1 page. ;)
>>
>> Hum, not so sure now ;)
>> I got confused, only the header is one page.
>> The test is working as a best effort, and don't cover the case where
>> only few pages inside the VDSO are unmmapped (start >
>> mm->context.vdso_base). This is not what CRIU is doing and so this was
>> enough for CRIU support.
>>
>> Michael, do you think there is a need to manage all the possibility
>> here, since the only user is CRIU and unmapping the VDSO is not a so
>> good idea for other processes ?
> 
> Couldn't we implement the semantic that if any part of the VDSO is
> unmapped then vdso_base is set to zero? That should be fairly easy, eg:
> 
> 	if (start < vdso_end && end >= mm->context.vdso_base)
> 		mm->context.vdso_base = 0;
> 
> 
> We might need to add vdso_end to the mm->context, but that should be OK.
> 
> That seems like it would work for CRIU and make sense in general?

Sorry for the late answer, yes this would make more sense.

Here is a patch doing that.

Cheers,
Laurent