[3.13.y-ckt stable] Patch "arm64: Do not attempt to use init_mm in reset_context()" has been added to staging queue

[Kamal Mostafa]

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

    arm64: Do not attempt to use init_mm in reset_context()

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt24.

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

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From dff58d22824abc8a3a8210e13492f702025c42aa Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas at arm.com>
Date: Fri, 12 Jun 2015 11:24:41 +0100
Subject: arm64: Do not attempt to use init_mm in reset_context()

commit 565630d503ef24e44c252bed55571b3a0d68455f upstream.

After secondary CPU boot or hotplug, the active_mm of the idle thread is
&init_mm. The init_mm.pgd (swapper_pg_dir) is only meant for TTBR1_EL1
and must not be set in TTBR0_EL1. Since when active_mm == &init_mm the
TTBR0_EL1 is already set to the reserved value, there is no need to
perform any context reset.

Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm64/mm/context.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index baa758d..76c1e6c 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -92,6 +92,14 @@ static void reset_context(void *info)
 	unsigned int cpu = smp_processor_id();
 	struct mm_struct *mm = current->active_mm;

+	/*
+	 * current->active_mm could be init_mm for the idle thread immediately
+	 * after secondary CPU boot or hotplug. TTBR0_EL1 is already set to
+	 * the reserved value, so no need to reset any context.
+	 */
+	if (mm == &init_mm)
+		return;
+
 	smp_rmb();
 	asid = cpu_last_asid + cpu;

--
1.9.1