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:
- 'start' and 'end' are page aligned (this is guaranteed by __do_munmap().
- 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?
cheers