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Subject[PATCH 3.14 34/38] arm64: Use the reserved TTBR0 if context switching to the init_mm
Date
3.14-stable review patch.  If anyone has any objections, please let me know.

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

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

commit e53f21bce4d35a93b23d8fa1a840860f6c74f59e upstream.

The idle_task_exit() function may call switch_mm() with next ==
&init_mm. On arm64, init_mm.pgd cannot be used for user mappings, so
this patch simply sets the reserved TTBR0.

Reported-by: Jon Medhurst (Tixy) <tixy@linaro.org>
Tested-by: Jon Medhurst (Tixy) <tixy@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/include/asm/mmu_context.h | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -151,6 +151,15 @@ switch_mm(struct mm_struct *prev, struct
{
unsigned int cpu = smp_processor_id();

+ /*
+ * init_mm.pgd does not contain any user mappings and it is always
+ * active for kernel addresses in TTBR1. Just set the reserved TTBR0.
+ */
+ if (next == &init_mm) {
+ cpu_set_reserved_ttbr0();
+ return;
+ }
+
if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next)) || prev != next)
check_and_switch_context(next, tsk);
}



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