kfence, x86: fix preemptible warning on KPTI-enabled systems

On systems with KPTI enabled, we can currently observe the following

  BUG: using smp_processor_id() in preemptible
  caller is invalidate_user_asid+0x13/0x50
  CPU: 6 PID: 1075 Comm: dmesg Not tainted 5.12.0-rc4-gda4a2b1a5479-kfence_1+ #1
  Hardware name: Hewlett-Packard HP Pro 3500 Series/2ABF, BIOS 8.11 10/24/2012
  Call Trace:

While it normally makes sense to require preemption to be off, so that
the expected CPU's TLB is flushed and not another, in our case it really
is best-effort (see comments in kfence_protect_page()).

Avoid the warning by disabling preemption around flush_tlb_one_kernel().

Link: https://lore.kernel.org/lkml/YGIDBAboELGgMgXy@elver.google.com/
Link: https://lkml.kernel.org/r/20210330065737.652669-1-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reported-by: Tomi Sarvela <tomi.p.sarvela@intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed