[PATCH v4 4/5] ARM: smp: Store current pointer in TPIDRURO register if available

[Russell King (Oracle)]

On Mon, Sep 13, 2021 at 12:40:00PM +0200, Ard Biesheuvel wrote:
> @@ -767,13 +769,18 @@ ENTRY(__switch_to)
>  	mcr	p15, 0, r6, c3, c0, 0		@ Set domain register
>  #endif
>  	mov	r5, r0
> -	add	r4, r2, #TI_CPU_SAVE
> +	mov	r4, r2
>  	ldr	r0, =thread_notify_head
>  	mov	r1, #THREAD_NOTIFY_SWITCH
>  	bl	atomic_notifier_call_chain
>  #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)
>  	str	r7, [r8]
>  #endif
> +#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
> +	ldr	ip, [r4, #TI_TASK]
> +	set_current ip
> +#endif
> +	add	r4, r4, #TI_CPU_SAVE
>   THUMB(	mov	ip, r4			   )
>  	mov	r0, r5
>   ARM(	ldmia	r4, {r4 - sl, fp, sp, pc}  )	@ Load all regs saved previously

I would like to keep this as optimal as possible, and the setting of
TPIDRURO to be as close to the stack pointer change too, so I'd
suggest a slightly different approach:

	switch_tls r1, r4, r5, r3, r7
+#if (defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)) || \
+    defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO)
+	ldr	r9, [r2, #TI_TASK]
+#endif
#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)
-	ldr	r7, [r2, #TI_TASK]
	ldr	r8, =__stack_chk_guard
	.if (TSK_STACK_CANARY > IMM12_MASK)
-	add	r7, r7, #TSK_STACK_CANARY & ~IMM12_MASK
-	.endif
+	add	r7, r9, #TSK_STACK_CANARY & ~IMM12_MASK
	ldr	r7, [r7, #TSK_STACK_CANARY & IMM12_MASK]
+	.else
+	ldr	r7, [r9, #TSK_STACK_CANARY & IMM12_MASK]
+	.endif
#endif
...
	mov	r0, r5
+#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
+	set_current r9
+#endif
 ARM(	ldmia	r4, {r4 - sl, fp, sp, pc}  )	@ Load all regs saved previously

It's a slightly more complex change, but one I think we should do.

-- 
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