[Xenial PATCH] arm64: mm: avoid calling apply_to_page_range on empty range

[Ming Lei]

From: Mika Penttilä <mika.penttila at nextfour.com>

Calling apply_to_page_range with an empty range results in a BUG_ON
from the core code. This can be triggered by trying to load the st_drv
module with CONFIG_DEBUG_SET_MODULE_RONX enabled:

  kernel BUG at mm/memory.c:1874!
  Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
  Modules linked in:
  CPU: 3 PID: 1764 Comm: insmod Not tainted 4.5.0-rc1+ #2
  Hardware name: ARM Juno development board (r0) (DT)
  task: ffffffc9763b8000 ti: ffffffc975af8000 task.ti: ffffffc975af8000
  PC is at apply_to_page_range+0x2cc/0x2d0
  LR is at change_memory_common+0x80/0x108

This patch fixes the issue by making change_memory_common (called by the
set_memory_* functions) a NOP when numpages == 0, therefore avoiding the
erroneous call to apply_to_page_range and bringing us into line with x86
and s390.

BugLink: http://bugs.launchpad.net/bugs/1547718
Cc: <stable at vger.kernel.org>
Reviewed-by: Laura Abbott <labbott at redhat.com>
Acked-by: David Rientjes <rientjes at google.com>
Signed-off-by: Mika Penttilä <mika.penttila at nextfour.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
(cherry picked from commit 57adec866c0440976c96a4b8f5b59fb411b1cacb)
Signed-off-by: Ming Lei <ming.lei at canonical.com>
---
 arch/arm64/mm/pageattr.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 3571c73..cf62407 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -57,6 +57,9 @@ static int change_memory_common(unsigned long addr, int numpages,
 	if (end < MODULES_VADDR || end >= MODULES_END)
 		return -EINVAL;
 
+	if (!numpages)
+		return 0;
+
 	data.set_mask = set_mask;
 	data.clear_mask = clear_mask;
 
-- 
1.9.1