x86/vdso: Make the PER_CPU segment start out accessed
x86/vdso: Make the PER_CPU segment start out accessed

The first userspace attempt to read or write the PER_CPU segment
will write the accessed bit to the GDT.  This is visible to
userspace using the LAR instruction, and it also pointlessly
dirties a cache line.

Set the segment's accessed bit at boot to prevent userspace
access to segments from having side effects.

Signed-off-by: Andy Lutomirski <2cc0d0d76de2e6f37b92deeb83c85cb306fc5dc1@amacapital.net>
Link: http://lkml.kernel.org/r/ac63814ca4c637a08ec2fd0360d67ca67560a9ee.1411494540.git.2cc0d0d76de2e6f37b92deeb83c85cb306fc5dc1@amacapital.net
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs