linux-kernel - [RFC PATCH 4/6] arm64: pass stack base to secondary_start

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Date:   Wed, 12 Jul 2017 23:33:01 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     ard.biesheuvel@...aro.org, kernel-hardening@...ts.openwall.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     akashi.takahiro@...aro.org, catalin.marinas@....com,
        dave.martin@....com, james.morse@....com,
        labbott@...oraproject.org, will.deacon@....com,
        keescook@...omium.org, Mark Rutland <mark.rutland@....com>
Subject: [RFC PATCH 4/6] arm64: pass stack base to secondary_start_kernel

In subsequent patches, we'll want the base of the secondary stack in
secondary_start_kernel.

Pass the stack base down, as we do in the primary path, and add the
offset in secondary_start_kernel. Unfortunately, we can't encode
STACK_START_SP in an add immediate, so use a mov immedaite, which has
greater range.

This is far from a hot path, so the overhead shouldn't matter.

Signed-off-by: Mark Rutland <mark.rutland@....com>
---
 arch/arm64/kernel/head.S | 3 ++-
 arch/arm64/kernel/smp.c  | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index a58ecda..db77cac 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -613,7 +613,8 @@ __secondary_switched:
 
 	adr_l	x0, secondary_data
 	ldr	x1, [x0, #CPU_BOOT_STACK]	// get secondary_data.stack
-	mov	sp, x1
+	mov	x3, #THREAD_START_SP
+	add	sp, x1, x3
 	ldr	x2, [x0, #CPU_BOOT_TASK]
 	msr	tpidr_el1, x2
 	mov	x29, #0
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 6e0e16a..269c957 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -154,7 +154,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	 * page tables.
 	 */
 	secondary_data.task = idle;
-	secondary_data.stack = task_stack_page(idle) + THREAD_START_SP;
+	secondary_data.stack = task_stack_page(idle);
 	update_cpu_boot_status(CPU_MMU_OFF);
 	__flush_dcache_area(&secondary_data, sizeof(secondary_data));
 
-- 
1.9.1