linux-kernel - [PATCH 3.19.y-ckt 108/251] arm64: Do not attempt to use init_mm in reset

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Message-Id: <1437008972-9140-109-git-send-email-kamal@canonical.com>
Date:	Wed, 15 Jul 2015 18:07:09 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 108/251] arm64: Do not attempt to use init_mm in reset_context()

3.19.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Catalin Marinas <catalin.marinas@....com>

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@....com>
Signed-off-by: Kamal Mostafa <kamal@...onical.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

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