Currently, kernel context and interrupts are handled using a single kernel stack navigated by sp_el1. This forces many systems to use 16KB stack, not 8KB one. Low memory platforms naturally 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 trace struct thread_info using sp_el0 instead of sp_el1. This approach helps arm64 align with other architectures regarding object_is_on_stack() without additional complexity. Cc: James Morse <[email protected]> Signed-off-by: Jungseok Lee <[email protected]> --- 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/include/asm/irq.h | 8 +++ arch/arm64/include/asm/thread_info.h | 7 +- arch/arm64/kernel/asm-offsets.c | 5 ++ arch/arm64/kernel/entry.S | 54 ++++++++++++++-- arch/arm64/kernel/head.S | 3 + arch/arm64/kernel/irq.c | 21 ++++++ arch/arm64/kernel/smp.c | 6 ++ 7 files changed, 95 insertions(+), 9 deletions(-) diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h index bbb251b..67975a2 100644 --- a/arch/arm64/include/asm/irq.h +++ b/arch/arm64/include/asm/irq.h @@ -5,11 +5,19 @@ #include <asm-generic/irq.h> +struct irq_stack { + void *stack; + unsigned long thread_sp; + unsigned int count; +}; + struct pt_regs; extern void migrate_irqs(void); 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) { /* diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h index dcd06d1..44839c0 100644 --- a/arch/arm64/include/asm/thread_info.h +++ b/arch/arm64/include/asm/thread_info.h @@ -73,8 +73,11 @@ static inline struct thread_info *current_thread_info(void) __attribute_const__; static inline struct thread_info *current_thread_info(void) { - return (struct thread_info *) - (current_stack_pointer & ~(THREAD_SIZE - 1)); + unsigned long sp_el0; + + asm volatile("mrs %0, sp_el0" : "=r" (sp_el0)); + + return (struct thread_info *)(sp_el0 & ~(THREAD_SIZE - 1)); } #define thread_saved_pc(tsk) \ diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c index 8d89cf8..3bb5ce0 100644 --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -22,6 +22,7 @@ #include <linux/mm.h> #include <linux/dma-mapping.h> #include <linux/kvm_host.h> +#include <asm/irq.h> #include <asm/thread_info.h> #include <asm/memory.h> #include <asm/smp_plat.h> @@ -41,6 +42,10 @@ int main(void) BLANK(); DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, thread.cpu_context)); BLANK(); + DEFINE(IRQ_STACK, offsetof(struct irq_stack, stack)); + DEFINE(IRQ_THREAD_SP, offsetof(struct irq_stack, thread_sp)); + DEFINE(IRQ_COUNT, offsetof(struct irq_stack, count)); + BLANK(); DEFINE(S_X0, offsetof(struct pt_regs, regs[0])); DEFINE(S_X1, offsetof(struct pt_regs, regs[1])); DEFINE(S_X2, offsetof(struct pt_regs, regs[2])); diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 4306c93..c156540 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -88,7 +88,7 @@ .if \el == 0 mrs x21, sp_el0 - get_thread_info tsk // Ensure MDSCR_EL1.SS is clear, + get_thread_info \el, tsk // 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 @@ -105,6 +105,8 @@ .if \el == 0 mvn x21, xzr str x21, [sp, #S_SYSCALLNO] + mov x25, sp + msr sp_el0, x25 .endif /* @@ -163,9 +165,45 @@ alternative_endif eret // return to kernel .endm - .macro get_thread_info, rd + .macro get_thread_info, el, rd + .if \el == 0 mov \rd, sp - and \rd, \rd, #~(THREAD_SIZE - 1) // top of stack + .else + mrs \rd, sp_el0 + .endif + and \rd, \rd, #~(THREAD_SIZE - 1) // bottom of thread stack + .endm + + .macro get_irq_stack + adr_l x21, irq_stacks + mrs x22, tpidr_el1 + add x21, x21, x22 + .endm + + .macro irq_stack_entry + get_irq_stack + ldr w23, [x21, #IRQ_COUNT] + cbnz w23, 1f // check irq recursion + mov x23, sp + str x23, [x21, #IRQ_THREAD_SP] + ldr x23, [x21, #IRQ_STACK] + mov sp, x23 + mov x23, xzr +1: add w23, w23, #1 + str w23, [x21, #IRQ_COUNT] + .endm + + .macro irq_stack_exit + get_irq_stack + ldr w23, [x21, #IRQ_COUNT] + sub w23, w23, #1 + cbnz w23, 1f // check irq recursion + mov x23, sp + str x23, [x21, #IRQ_STACK] + ldr x23, [x21, #IRQ_THREAD_SP] + mov sp, x23 + mov x23, xzr +1: str w23, [x21, #IRQ_COUNT] .endm /* @@ -183,10 +221,11 @@ 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 @@ -361,7 +400,7 @@ el1_irq: irq_handler #ifdef CONFIG_PREEMPT - get_thread_info tsk + get_thread_info 1, tsk ldr w24, [tsk, #TI_PREEMPT] // get preempt count cbnz w24, 1f // preempt count != 0 ldr x0, [tsk, #TI_FLAGS] // get flags @@ -597,6 +636,7 @@ ENTRY(cpu_switch_to) ldp x29, x9, [x8], #16 ldr lr, [x8] mov sp, x9 + msr sp_el0, x9 ret ENDPROC(cpu_switch_to) @@ -655,7 +695,7 @@ ENTRY(ret_from_fork) cbz x19, 1f // not a kernel thread mov x0, x20 blr x19 -1: get_thread_info tsk +1: get_thread_info 1, tsk b ret_to_user ENDPROC(ret_from_fork) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index a055be6..cb13290 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -441,6 +441,8 @@ __mmap_switched: b 1b 2: adr_l sp, initial_sp, x4 + mov x4, sp + msr sp_el0, x4 str_l x21, __fdt_pointer, x5 // Save FDT pointer str_l x24, memstart_addr, x6 // Save PHYS_OFFSET mov x29, #0 @@ -613,6 +615,7 @@ ENDPROC(secondary_startup) ENTRY(__secondary_switched) ldr x0, [x21] // get secondary_data.stack mov sp, x0 + msr sp_el0, x0 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 11dc3fd..88acb63 100644 --- a/arch/arm64/kernel/irq.c +++ b/arch/arm64/kernel/irq.c @@ -31,6 +31,8 @@ unsigned long irq_err_count; +DEFINE_PER_CPU(struct irq_stack, irq_stacks); + int arch_show_interrupts(struct seq_file *p, int prec) { show_ipi_list(p, prec); @@ -50,6 +52,9 @@ void __init set_handle_irq(void (*handle_irq)(struct pt_regs *)) void __init init_IRQ(void) { + if (alloc_irq_stack(smp_processor_id())) + panic("Failed to allocate IRQ stack for boot cpu"); + irqchip_init(); if (!handle_arch_irq) panic("No interrupt controller found."); @@ -115,3 +120,19 @@ void migrate_irqs(void) local_irq_restore(flags); } #endif /* CONFIG_HOTPLUG_CPU */ + +int alloc_irq_stack(unsigned int cpu) +{ + void *stack; + + if (per_cpu(irq_stacks, cpu).stack) + return 0; + + stack = (void *)__get_free_pages(THREADINFO_GFP, THREAD_SIZE_ORDER); + if (!stack) + return -ENOMEM; + + per_cpu(irq_stacks, cpu).stack = stack + THREAD_START_SP; + + return 0; +} diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index dbdaacd..0bd7049 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -97,6 +97,12 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle) secondary_data.stack = task_stack_page(idle) + THREAD_START_SP; __flush_dcache_area(&secondary_data, sizeof(secondary_data)); + 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. */ -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
