[PATCH v4 2/5] ARM: smp: Pass task to secondary_start_kernel

From: Ard Biesheuvel <ardb@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Keith Packard <keithpac@amazon.com>,
	Russell King <linux@armlinux.org.uk>,
	Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: [PATCH v4 2/5] ARM: smp: Pass task to secondary_start_kernel
Date: Mon, 13 Sep 2021 12:39:58 +0200	[thread overview]
Message-ID: <20210913104001.3043132-3-ardb@kernel.org> (raw)
In-Reply-To: <20210913104001.3043132-1-ardb@kernel.org>

From: Keith Packard <keithpac@amazon.com>

This avoids needing to compute the task pointer in this function, which
will no longer be possible once we move thread_info off the stack.

Signed-off-by: Keith Packard <keithpac@amazon.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/include/asm/smp.h   | 3 ++-
 arch/arm/kernel/head-nommu.S | 1 +
 arch/arm/kernel/head.S       | 5 +++--
 arch/arm/kernel/smp.c        | 8 ++++++--
 4 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
index 5d508f5d56c4..f16cbbd5cda4 100644
--- a/arch/arm/include/asm/smp.h
+++ b/arch/arm/include/asm/smp.h
@@ -48,7 +48,7 @@ extern void set_smp_ipi_range(int ipi_base, int nr_ipi);
  * Called from platform specific assembly code, this is the
  * secondary CPU entry point.
  */
-asmlinkage void secondary_start_kernel(void);
+asmlinkage void secondary_start_kernel(struct task_struct *task);
 
 
 /*
@@ -61,6 +61,7 @@ struct secondary_data {
 	};
 	unsigned long swapper_pg_dir;
 	void *stack;
+	struct task_struct *task;
 };
 extern struct secondary_data secondary_data;
 extern void secondary_startup(void);
diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
index 0fc814bbc34b..fadfee9e2b45 100644
--- a/arch/arm/kernel/head-nommu.S
+++ b/arch/arm/kernel/head-nommu.S
@@ -115,6 +115,7 @@ ENTRY(secondary_startup)
 	ret	r12
 1:	bl	__after_proc_init
 	ldr	sp, [r7, #12]			@ set up the stack pointer
+	ldr	r0, [r7, #16]			@ set up task pointer
 	mov	fp, #0
 	b	secondary_start_kernel
 ENDPROC(secondary_startup)
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 29070eb8df7d..fa44e2d9f0b0 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -424,8 +424,9 @@ ENDPROC(secondary_startup)
 ENDPROC(secondary_startup_arm)
 
 ENTRY(__secondary_switched)
-	ldr_l	r7, secondary_data + 12		@ get secondary_data.stack
-	mov	sp, r7
+	adr_l	r7, secondary_data + 12		@ get secondary_data.stack
+	ldr	sp, [r7]
+	ldr	r0, [r7, #4]			@ get secondary_data.task
 	mov	fp, #0
 	b	secondary_start_kernel
 ENDPROC(__secondary_switched)
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 842427ff2b3c..8979d548ec17 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -153,6 +153,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	secondary_data.pgdir = virt_to_phys(idmap_pgd);
 	secondary_data.swapper_pg_dir = get_arch_pgd(swapper_pg_dir);
 #endif
+	secondary_data.task = idle;
 	sync_cache_w(&secondary_data);
 
 	/*
@@ -375,9 +376,12 @@ void arch_cpu_idle_dead(void)
 	 */
 	__asm__("mov	sp, %0\n"
 	"	mov	fp, #0\n"
+	"	mov	r0, %1\n"
 	"	b	secondary_start_kernel"
 		:
-		: "r" (task_stack_page(current) + THREAD_SIZE - 8));
+		: "r" (task_stack_page(current) + THREAD_SIZE - 8),
+		  "r" (current)
+		: "r0");
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
@@ -400,7 +404,7 @@ static void smp_store_cpu_info(unsigned int cpuid)
  * This is the secondary CPU boot entry.  We're using this CPUs
  * idle thread stack, but a set of temporary page tables.
  */
-asmlinkage void secondary_start_kernel(void)
+asmlinkage void secondary_start_kernel(struct task_struct *task)
 {
 	struct mm_struct *mm = &init_mm;
 	unsigned int cpu;
-- 
2.30.2


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