[3.16.y-ckt stable] Patch "arm64: head.S: ensure visibility of page tables" has been added to staging queue

[Luis Henriques]

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

    arm64: head.S: ensure visibility of page tables

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt11.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 00797ccf07b6aa755cf2d81fa38a8bd93eed83f6 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland at arm.com>
Date: Tue, 24 Mar 2015 13:50:27 +0000
Subject: arm64: head.S: ensure visibility of page tables

commit 91d57155dc5ab4b311624b7ee570339b6af19ad5 upstream.

After writing the page tables, we use __inval_cache_range to invalidate
any stale cache entries. Strongly Ordered memory accesses are not
ordered w.r.t. cache maintenance instructions, and hence explicit memory
barriers are required to provide this ordering. However,
__inval_cache_range was written to be used on Normal Cacheable memory
once the MMU and caches are on, and does not have any barriers prior to
the DC instructions.

This patch adds a DMB between the page tables being written and the
corresponding cachelines being invalidated, ensuring that the
invalidation makes the new data visible to subsequent cacheable
accesses. A barrier is not required before the prior invalidate as we do
not access the page table memory area prior to this, and earlier
barriers in preserve_boot_args and set_cpu_boot_mode_flag ensures
ordering w.r.t. any stores performed prior to entering Linux.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
Fixes: c218bca74eeafa2f ("arm64: Relax the kernel cache requirements for boot")
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arm64/kernel/head.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index a2c1195abb7f..1cd11e73058f 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -599,6 +599,7 @@ __create_page_tables:
 	 */
 	mov	x0, x25
 	add	x1, x26, #SWAPPER_DIR_SIZE
+	dmb	sy
 	bl	__inval_cache_range

 	mov	lr, x27