Messages in this thread Patch in this message | | | From | Jungseok Lee <> | Subject | [PATCH v5] arm64: Introduce IRQ stack | Date | Sat, 17 Oct 2015 14:27:33 +0000 |
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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 <takahiro.akashi@linaro.org> Cc: James Morse <james.morse@arm.com> Signed-off-by: Jungseok Lee <jungseoklee85@gmail.com> --- 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 + 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); -- 2.5.0
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