Subject: [PATCH v5] arm64: Introduce IRQ stack

From: [email-masked] (AKASHI Takahiro)
Date: Mon, 19 Oct 2015 15:54:57 +0900

On 10/17/2015 11:27 PM, Jungseok Lee wrote:
> Currently, kernel context and interrupts are handled using a single
> kernel stack navigated by sp_el1. This forces a system to use 16KB
> stack, not 8KB one. This restriction makes low memory platforms
> suffer from memory pressure accompanied by performance degradation.
>
> This patch addresses the issue as introducing a separate percpu IRQ
> stack to handle both hard and soft interrupts with two ground rules:
>
>    - Utilize sp_el0 in EL1 context, which is not used currently
>    - Do not complicate current_thread_info calculation
>
> It is a core concept to directly retrieve struct thread_info from
> sp_el0. This approach helps to prevent text section size from being
> increased largely as removing masking operation using THREAD_SIZE
> in tons of places.
>
> [Thanks to James Morse for his valuable feedbacks which greatly help
> to figure out a better implementation. - Jungseok]
>
> Cc: AKASHI Takahiro <[email-masked]>
> Cc: James Morse <[email-masked]>
> Signed-off-by: Jungseok Lee <[email-masked]>
> ---
> I've used Cc', not Tested-by tag, from James, since there is a gap
> between v4 and v5.
>
> Changes since v4:
> - Supported 64KB page system
> - Introduced IRQ_STACK_* macro, per Catalin
> - Rebased on top of for-next/core
>
> Changes since v3:
> - Expanded stack trace to support IRQ stack
> - Added more comments
>
> Changes since v2:
> - Optmised current_thread_info function as removing masking operation
>    and volatile keyword, per James and Catalin
> - Reworked irq re-enterance check logic using top-bit comparison of
>    stacks, per James
> - Added sp_el0 update in cpu_resume, per James
> - Selected HAVE_IRQ_EXIT_ON_IRQ_STACK to expose this feature explicitly
> - Added a Tested-by tag from James
> - Added comments on sp_el0 as a helper messeage
>
> Changes since v1:
> - Rebased on top of v4.3-rc1
> - Removed Kconfig about IRQ stack, per James
> - Used PERCPU for IRQ stack, per James
> - Tried to allocate IRQ stack when CPU is about to start up, per James
> - Moved sp_el0 update into kernel_entry macro, per James
> - Dropped S_SP removal patch, per Mark and James
>
>   arch/arm64/Kconfig                   |  1 +
>   arch/arm64/include/asm/irq.h         | 27 ++++++++++
>   arch/arm64/include/asm/thread_info.h | 10 +++-
>   arch/arm64/kernel/entry.S            | 42 ++++++++++++++--
>   arch/arm64/kernel/head.S             |  5 ++
>   arch/arm64/kernel/irq.c              | 24 +++++++++
>   arch/arm64/kernel/sleep.S            |  3 ++
>   arch/arm64/kernel/smp.c              | 13 ++++-
>   8 files changed, 116 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 2782c11..3855fd2 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -69,6 +69,7 @@ config ARM64
>   	select HAVE_FUNCTION_GRAPH_TRACER
>   	select HAVE_GENERIC_DMA_COHERENT
>   	select HAVE_HW_BREAKPOINT if PERF_EVENTS
> +	select HAVE_IRQ_EXIT_ON_IRQ_STACK
>   	select HAVE_MEMBLOCK
>   	select HAVE_PATA_PLATFORM
>   	select HAVE_PERF_EVENTS
> diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
> index 0916929..2755b2f 100644
> --- a/arch/arm64/include/asm/irq.h
> +++ b/arch/arm64/include/asm/irq.h
> @@ -1,14 +1,40 @@
>   #ifndef __ASM_IRQ_H
>   #define __ASM_IRQ_H
>
> +#ifndef CONFIG_ARM64_64K_PAGES
> +#define IRQ_STACK_SIZE_ORDER	2
> +#endif
> +
> +#define IRQ_STACK_SIZE		16384
> +#define IRQ_STACK_START_SP	(IRQ_STACK_SIZE - 16)
> +
> +#ifndef __ASSEMBLY__
> +
> +#include <linux/gfp.h>
>   #include <linux/irqchip/arm-gic-acpi.h>
> +#include <linux/slab.h>
>
>   #include <asm-generic/irq.h>
>
> +#if IRQ_STACK_SIZE >= PAGE_SIZE
> +static inline void *__alloc_irq_stack(void)
> +{
> +       return (void *)__get_free_pages(THREADINFO_GFP | __GFP_ZERO,
> +                                       IRQ_STACK_SIZE_ORDER);
> +}
> +#else
> +static inline void *__alloc_irq_stack(void)
> +{
> +       return kmalloc(IRQ_STACK_SIZE, THREADINFO_GFP | __GFP_ZERO);
> +}
> +#endif
> +

Spaces are at the beginning of lines.
and it seems that this patch cannot be cleanly applied.

-Takahiro AKASHI

>   struct pt_regs;
>
>   extern void set_handle_irq(void (*handle_irq)(struct pt_regs *));
>
> +extern int alloc_irq_stack(unsigned int cpu);
> +
>   static inline void acpi_irq_init(void)
>   {
>   	/*
> @@ -21,3 +47,4 @@ static inline void acpi_irq_init(void)
>   #define acpi_irq_init acpi_irq_init
>
>   #endif
> +#endif
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index 555c6de..7b2f2ec 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -71,10 +71,16 @@ register unsigned long current_stack_pointer asm ("sp");
>    */
>   static inline struct thread_info *current_thread_info(void) __attribute_const__;
>
> +/*
> + * struct thread_info can be accessed directly via sp_el0.
> + */
>   static inline struct thread_info *current_thread_info(void)
>   {
> -	return (struct thread_info *)
> -		(current_stack_pointer & ~(THREAD_SIZE - 1));
> +	unsigned long sp_el0;
> +
> +	asm ("mrs %0, sp_el0" : "=r" (sp_el0));
> +
> +	return (struct thread_info *)sp_el0;
>   }
>
>   #define thread_saved_pc(tsk)	\
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 4306c93..c8e0bcf 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -27,6 +27,7 @@
>   #include <asm/cpufeature.h>
>   #include <asm/errno.h>
>   #include <asm/esr.h>
> +#include <asm/irq.h>
>   #include <asm/thread_info.h>
>   #include <asm/unistd.h>
>
> @@ -88,7 +89,8 @@
>
>   	.if	\el == 0
>   	mrs	x21, sp_el0
> -	get_thread_info tsk			// Ensure MDSCR_EL1.SS is clear,
> +	mov	tsk, sp
> +	and	tsk, tsk, #~(THREAD_SIZE - 1)	// Ensure MDSCR_EL1.SS is clear,
>   	ldr	x19, [tsk, #TI_FLAGS]		// since we can unmask debug
>   	disable_step_tsk x19, x20		// exceptions when scheduling.
>   	.else
> @@ -108,6 +110,13 @@
>   	.endif
>
>   	/*
> +	 * Set sp_el0 to current thread_info.
> +	 */
> +	.if	\el == 0
> +	msr	sp_el0, tsk
> +	.endif
> +
> +	/*
>   	 * Registers that may be useful after this macro is invoked:
>   	 *
>   	 * x21 - aborted SP
> @@ -164,8 +173,28 @@ alternative_endif
>   	.endm
>
>   	.macro	get_thread_info, rd
> -	mov	\rd, sp
> -	and	\rd, \rd, #~(THREAD_SIZE - 1)	// top of stack
> +	mrs	\rd, sp_el0
> +	.endm
> +
> +	.macro	irq_stack_entry
> +	adr_l	x19, irq_stacks
> +	mrs	x20, tpidr_el1
> +	add	x19, x19, x20
> +	ldr	x24, [x19]
> +	and	x20, x24, #~(IRQ_STACK_SIZE - 1)
> +	mov	x23, sp
> +	and	x23, x23, #~(IRQ_STACK_SIZE - 1)
> +	cmp	x20, x23			// check irq re-enterance
> +	mov	x19, sp
> +	csel	x23, x19, x24, eq		// x24 = top of irq stack
> +	mov	sp, x23
> +	.endm
> +
> +	/*
> +	 * x19 is preserved between irq_stack_entry and irq_stack_exit.
> +	 */
> +	.macro	irq_stack_exit
> +	mov	sp, x19
>   	.endm
>
>   /*
> @@ -183,10 +212,11 @@ tsk	.req	x28		// current thread_info
>    * Interrupt handling.
>    */
>   	.macro	irq_handler
> -	adrp	x1, handle_arch_irq
> -	ldr	x1, [x1, #:lo12:handle_arch_irq]
> +	ldr_l	x1, handle_arch_irq
>   	mov	x0, sp
> +	irq_stack_entry
>   	blr	x1
> +	irq_stack_exit
>   	.endm
>
>   	.text
> @@ -597,6 +627,8 @@ ENTRY(cpu_switch_to)
>   	ldp	x29, x9, [x8], #16
>   	ldr	lr, [x8]
>   	mov	sp, x9
> +	and	x9, x9, #~(THREAD_SIZE - 1)
> +	msr	sp_el0, x9
>   	ret
>   ENDPROC(cpu_switch_to)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 2a8c1d5..eece484 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -441,6 +441,9 @@ __mmap_switched:
>   	b	1b
>   2:
>   	adr_l	sp, initial_sp, x4
> +	mov	x4, sp
> +	and	x4, x4, #~(THREAD_SIZE - 1)
> +	msr	sp_el0, x4			// Save thread_info
>   	str_l	x21, __fdt_pointer, x5		// Save FDT pointer
>   	str_l	x24, memstart_addr, x6		// Save PHYS_OFFSET
>   	mov	x29, #0
> @@ -621,6 +624,8 @@ ENDPROC(secondary_startup)
>   ENTRY(__secondary_switched)
>   	ldr	x0, [x21]			// get secondary_data.stack
>   	mov	sp, x0
> +	and	x0, x0, #~(THREAD_SIZE - 1)
> +	msr	sp_el0, x0			// save thread_info
>   	mov	x29, #0
>   	b	secondary_start_kernel
>   ENDPROC(__secondary_switched)
> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
> index 9f17ec0..13fe8f4 100644
> --- a/arch/arm64/kernel/irq.c
> +++ b/arch/arm64/kernel/irq.c
> @@ -30,6 +30,8 @@
>
>   unsigned long irq_err_count;
>
> +DEFINE_PER_CPU(void *, irq_stacks);
> +
>   int arch_show_interrupts(struct seq_file *p, int prec)
>   {
>   	show_ipi_list(p, prec);
> @@ -47,9 +49,31 @@ void __init set_handle_irq(void (*handle_irq)(struct pt_regs *))
>   	handle_arch_irq = handle_irq;
>   }
>
> +static char boot_irq_stack[IRQ_STACK_SIZE] __aligned(IRQ_STACK_SIZE);
> +
>   void __init init_IRQ(void)
>   {
> +	unsigned int cpu = smp_processor_id();
> +
> +	per_cpu(irq_stacks, cpu) = boot_irq_stack + IRQ_STACK_START_SP;
> +
>   	irqchip_init();
>   	if (!handle_arch_irq)
>   		panic("No interrupt controller found.");
>   }
> +
> +int alloc_irq_stack(unsigned int cpu)
> +{
> +	void *stack;
> +
> +	if (per_cpu(irq_stacks, cpu))
> +		return 0;
> +
> +	stack = __alloc_irq_stack();
> +	if (!stack)
> +		return -ENOMEM;
> +
> +	per_cpu(irq_stacks, cpu) = stack + IRQ_STACK_START_SP;
> +
> +	return 0;
> +}
> diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
> index f586f7c..e33fe33 100644
> --- a/arch/arm64/kernel/sleep.S
> +++ b/arch/arm64/kernel/sleep.S
> @@ -173,6 +173,9 @@ ENTRY(cpu_resume)
>   	/* load physical address of identity map page table in x1 */
>   	adrp	x1, idmap_pg_dir
>   	mov	sp, x2
> +	/* save thread_info */
> +	and	x2, x2, #~(THREAD_SIZE - 1)
> +	msr	sp_el0, x2
>   	/*
>   	 * cpu_do_resume expects x0 to contain context physical address
>   	 * pointer and x1 to contain physical address of 1:1 page tables
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index b7a973d..519681d 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -91,13 +91,22 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
>   	int ret;
>
>   	/*
> -	 * We need to tell the secondary core where to find its stack and the
> -	 * page tables.
> +	 * We need to tell the secondary core where to find its process stack
> +	 * and the page tables.
>   	 */
>   	secondary_data.stack = task_stack_page(idle) + THREAD_START_SP;
>   	__flush_dcache_area(&secondary_data, sizeof(secondary_data));
>
>   	/*
> +	 * Allocate IRQ stack to handle both hard and soft interrupts.
> +	 */
> +	ret = alloc_irq_stack(cpu);
> +	if (ret) {
> +		pr_crit("CPU%u: failed to allocate IRQ stack\n", cpu);
> +		return ret;
> +	}
> +
> +	/*
>   	 * Now bring the CPU into our world.
>   	 */
>   	ret = boot_secondary(cpu, idle);
>