From: Catalin Marinas <catalin.marinas@arm.com>
Date: Mon, 23 Mar 2015 15:06:50 +0000 (+0000)
Subject: arm64: Use the reserved TTBR0 if context switching to the init_mm
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=e53f21bce4d35a93b23d8fa1a840860f6c74f59e;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git

arm64: Use the reserved TTBR0 if context switching to the init_mm

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.

Cc: <stable@vger.kernel.org>
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>
---

diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index a9eee33dfa62..101a42bde728 100644
--- 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 mm_struct *next,
 {
 	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);
 }