[3.19.y-ckt stable] Patch "arm64: mm: avoid calling apply_to_page_range on empty range" has been added to the 3.19.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    arm64: mm: avoid calling apply_to_page_range on empty range

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt15.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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>From 844fc3628781ddd6faf623f8e7874cc1f5db55b3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mika=20Penttil=C3=A4?= <mika.penttila at nextfour.com>
Date: Tue, 26 Jan 2016 15:47:25 +0000
Subject: arm64: mm: avoid calling apply_to_page_range on empty range
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commit 57adec866c0440976c96a4b8f5b59fb411b1cacb upstream.

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.

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>
Signed-off-by: Kamal Mostafa <kamal 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 bb0ea94..491acbb 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -54,6 +54,9 @@ static int change_memory_common(unsigned long addr, int numpages,
 	if (!is_module_address(start) || !is_module_address(end - 1))
 		return -EINVAL;

+	if (!numpages)
+		return 0;
+
 	data.set_mask = set_mask;
 	data.clear_mask = clear_mask;

--
1.9.1