From: Mark Rutland <mark.rutland@arm.com> To: linux-arm-kernel@lists.infradead.org Cc: ardb@kernel.org, bp@alien8.de, catalin.marinas@arm.com, dave.hansen@linux.intel.com, frederic@kernel.org, james.morse@arm.com, joey.gouly@arm.com, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, luto@kernel.org, mark.rutland@arm.com, mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, valentin.schneider@arm.com, will@kernel.org Subject: [PATCH v3 7/7] arm64: support PREEMPT_DYNAMIC Date: Wed, 9 Feb 2022 15:35:35 +0000 [thread overview] Message-ID: <20220209153535.818830-8-mark.rutland@arm.com> (raw) In-Reply-To: <20220209153535.818830-1-mark.rutland@arm.com> This patch enables support for PREEMPT_DYNAMIC on arm64, allowing the preemption model to be chosen at boot time. Specifically, this patch selects HAVE_PREEMPT_DYNAMIC_KEY, so that each preemption function is an out-of-line call with an early return depending upon a static key. This leaves almost all the codegen up to the compiler, and side-steps a number of pain points with static calls (e.g. interaction with CFI schemes). This should have no worse overhead than using non-inline static calls, as those use out-of-line trampolines with early returns. For example, the dynamic_cond_resched() wrapper looks as follows when enabled. When disabled, the first `B` is replaced with a `NOP`, resulting in an early return. | <dynamic_cond_resched>: | bti c | b <dynamic_cond_resched+0x10> // or `nop` | mov w0, #0x0 | ret | mrs x0, sp_el0 | ldr x0, [x0, #8] | cbnz x0, <dynamic_cond_resched+0x8> | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl <preempt_schedule_common> | mov w0, #0x1 | ldp x29, x30, [sp], #16 | autiasp | ret ... compared to the regular form of the function: | <__cond_resched>: | bti c | mrs x0, sp_el0 | ldr x1, [x0, #8] | cbz x1, <__cond_resched+0x18> | mov w0, #0x0 | ret | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl <preempt_schedule_common> | mov w0, #0x1 | ldp x29, x30, [sp], #16 | autiasp | ret Since arm64 does not yet use the generic entry code, we must define our own `sk_dynamic_irqentry_exit_cond_resched`, which will be enabled/disabled by the common code in kernel/sched/core.c. All other preemption functions and associated static keys are defined there. Note that PREEMPT_DYNAMIC is `def bool y`, so this will default to enabled. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Joey Gouly <joey.gouly@arm.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Valentin Schneider <valentin.schneider@arm.com> Cc: Will Deacon <will@kernel.org> --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/preempt.h | 19 +++++++++++++++++-- arch/arm64/kernel/entry-common.c | 10 +++++++++- 3 files changed, 27 insertions(+), 3 deletions(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index f2b5a4abef21..3831d922a81d 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -192,6 +192,7 @@ config ARM64 select HAVE_PERF_EVENTS select HAVE_PERF_REGS select HAVE_PERF_USER_STACK_DUMP + select HAVE_PREEMPT_DYNAMIC_KEY select HAVE_REGS_AND_STACK_ACCESS_API select HAVE_POSIX_CPU_TIMERS_TASK_WORK select HAVE_FUNCTION_ARG_ACCESS_API diff --git a/arch/arm64/include/asm/preempt.h b/arch/arm64/include/asm/preempt.h index e83f0982b99c..0159b625cc7f 100644 --- a/arch/arm64/include/asm/preempt.h +++ b/arch/arm64/include/asm/preempt.h @@ -2,6 +2,7 @@ #ifndef __ASM_PREEMPT_H #define __ASM_PREEMPT_H +#include <linux/jump_label.h> #include <linux/thread_info.h> #define PREEMPT_NEED_RESCHED BIT(32) @@ -80,10 +81,24 @@ static inline bool should_resched(int preempt_offset) } #ifdef CONFIG_PREEMPTION + void preempt_schedule(void); -#define __preempt_schedule() preempt_schedule() void preempt_schedule_notrace(void); -#define __preempt_schedule_notrace() preempt_schedule_notrace() + +#ifdef CONFIG_PREEMPT_DYNAMIC + +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +void dynamic_preempt_schedule(void); +#define __preempt_schedule() dynamic_preempt_schedule() +void dynamic_preempt_schedule_notrace(void); +#define __preempt_schedule_notrace() dynamic_preempt_schedule_notrace() + +#else /* CONFIG_PREEMPT_DYNAMIC */ + +#define __preempt_schedule() preempt_schedule() +#define __preempt_schedule_notrace() preempt_schedule_notrace() + +#endif /* CONFIG_PREEMPT_DYNAMIC */ #endif /* CONFIG_PREEMPTION */ #endif /* __ASM_PREEMPT_H */ diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index 2c639b6b676d..675352ec1368 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -220,9 +220,17 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs) lockdep_hardirqs_on(CALLER_ADDR0); } +#ifdef CONFIG_PREEMPT_DYNAMIC +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +#define need_irq_preemption() \ + (static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched)) +#else +#define need_irq_preemption() (IS_ENABLED(CONFIG_PREEMPTION)) +#endif + static void __sched arm64_preempt_schedule_irq(void) { - if (!IS_ENABLED(CONFIG_PREEMPTION)) + if (!need_irq_preemption()) return; /* -- 2.30.2
WARNING: multiple messages have this Message-ID (diff)
From: Mark Rutland <mark.rutland@arm.com> To: linux-arm-kernel@lists.infradead.org Cc: ardb@kernel.org, bp@alien8.de, catalin.marinas@arm.com, dave.hansen@linux.intel.com, frederic@kernel.org, james.morse@arm.com, joey.gouly@arm.com, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, luto@kernel.org, mark.rutland@arm.com, mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, valentin.schneider@arm.com, will@kernel.org Subject: [PATCH v3 7/7] arm64: support PREEMPT_DYNAMIC Date: Wed, 9 Feb 2022 15:35:35 +0000 [thread overview] Message-ID: <20220209153535.818830-8-mark.rutland@arm.com> (raw) In-Reply-To: <20220209153535.818830-1-mark.rutland@arm.com> This patch enables support for PREEMPT_DYNAMIC on arm64, allowing the preemption model to be chosen at boot time. Specifically, this patch selects HAVE_PREEMPT_DYNAMIC_KEY, so that each preemption function is an out-of-line call with an early return depending upon a static key. This leaves almost all the codegen up to the compiler, and side-steps a number of pain points with static calls (e.g. interaction with CFI schemes). This should have no worse overhead than using non-inline static calls, as those use out-of-line trampolines with early returns. For example, the dynamic_cond_resched() wrapper looks as follows when enabled. When disabled, the first `B` is replaced with a `NOP`, resulting in an early return. | <dynamic_cond_resched>: | bti c | b <dynamic_cond_resched+0x10> // or `nop` | mov w0, #0x0 | ret | mrs x0, sp_el0 | ldr x0, [x0, #8] | cbnz x0, <dynamic_cond_resched+0x8> | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl <preempt_schedule_common> | mov w0, #0x1 | ldp x29, x30, [sp], #16 | autiasp | ret ... compared to the regular form of the function: | <__cond_resched>: | bti c | mrs x0, sp_el0 | ldr x1, [x0, #8] | cbz x1, <__cond_resched+0x18> | mov w0, #0x0 | ret | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl <preempt_schedule_common> | mov w0, #0x1 | ldp x29, x30, [sp], #16 | autiasp | ret Since arm64 does not yet use the generic entry code, we must define our own `sk_dynamic_irqentry_exit_cond_resched`, which will be enabled/disabled by the common code in kernel/sched/core.c. All other preemption functions and associated static keys are defined there. Note that PREEMPT_DYNAMIC is `def bool y`, so this will default to enabled. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Joey Gouly <joey.gouly@arm.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Valentin Schneider <valentin.schneider@arm.com> Cc: Will Deacon <will@kernel.org> --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/preempt.h | 19 +++++++++++++++++-- arch/arm64/kernel/entry-common.c | 10 +++++++++- 3 files changed, 27 insertions(+), 3 deletions(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index f2b5a4abef21..3831d922a81d 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -192,6 +192,7 @@ config ARM64 select HAVE_PERF_EVENTS select HAVE_PERF_REGS select HAVE_PERF_USER_STACK_DUMP + select HAVE_PREEMPT_DYNAMIC_KEY select HAVE_REGS_AND_STACK_ACCESS_API select HAVE_POSIX_CPU_TIMERS_TASK_WORK select HAVE_FUNCTION_ARG_ACCESS_API diff --git a/arch/arm64/include/asm/preempt.h b/arch/arm64/include/asm/preempt.h index e83f0982b99c..0159b625cc7f 100644 --- a/arch/arm64/include/asm/preempt.h +++ b/arch/arm64/include/asm/preempt.h @@ -2,6 +2,7 @@ #ifndef __ASM_PREEMPT_H #define __ASM_PREEMPT_H +#include <linux/jump_label.h> #include <linux/thread_info.h> #define PREEMPT_NEED_RESCHED BIT(32) @@ -80,10 +81,24 @@ static inline bool should_resched(int preempt_offset) } #ifdef CONFIG_PREEMPTION + void preempt_schedule(void); -#define __preempt_schedule() preempt_schedule() void preempt_schedule_notrace(void); -#define __preempt_schedule_notrace() preempt_schedule_notrace() + +#ifdef CONFIG_PREEMPT_DYNAMIC + +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +void dynamic_preempt_schedule(void); +#define __preempt_schedule() dynamic_preempt_schedule() +void dynamic_preempt_schedule_notrace(void); +#define __preempt_schedule_notrace() dynamic_preempt_schedule_notrace() + +#else /* CONFIG_PREEMPT_DYNAMIC */ + +#define __preempt_schedule() preempt_schedule() +#define __preempt_schedule_notrace() preempt_schedule_notrace() + +#endif /* CONFIG_PREEMPT_DYNAMIC */ #endif /* CONFIG_PREEMPTION */ #endif /* __ASM_PREEMPT_H */ diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index 2c639b6b676d..675352ec1368 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -220,9 +220,17 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs) lockdep_hardirqs_on(CALLER_ADDR0); } +#ifdef CONFIG_PREEMPT_DYNAMIC +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +#define need_irq_preemption() \ + (static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched)) +#else +#define need_irq_preemption() (IS_ENABLED(CONFIG_PREEMPTION)) +#endif + static void __sched arm64_preempt_schedule_irq(void) { - if (!IS_ENABLED(CONFIG_PREEMPTION)) + if (!need_irq_preemption()) return; /* -- 2.30.2 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2022-02-09 15:36 UTC|newest] Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-02-09 15:35 [PATCH v3 0/7] arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys Mark Rutland 2022-02-09 15:35 ` Mark Rutland 2022-02-09 15:35 ` [PATCH v3 1/7] sched/preempt: move PREEMPT_DYNAMIC logic later Mark Rutland 2022-02-09 15:35 ` Mark Rutland 2022-02-09 15:35 ` [PATCH v3 2/7] sched/preempt: refactor sched_dynamic_update() Mark Rutland 2022-02-09 15:35 ` Mark Rutland 2022-02-09 15:35 ` [PATCH v3 3/7] sched/preempt: simplify irqentry_exit_cond_resched() callers Mark Rutland 2022-02-09 15:35 ` Mark Rutland 2022-02-09 15:35 ` [PATCH v3 4/7] sched/preempt: decouple HAVE_PREEMPT_DYNAMIC from GENERIC_ENTRY Mark Rutland 2022-02-09 15:35 ` Mark Rutland 2022-02-09 15:35 ` [PATCH v3 5/7] sched/preempt: add PREEMPT_DYNAMIC using static keys Mark Rutland 2022-02-09 15:35 ` Mark Rutland 2022-02-09 17:48 ` Frederic Weisbecker 2022-02-09 17:48 ` Frederic Weisbecker 2022-02-10 10:27 ` Mark Rutland 2022-02-10 10:27 ` Mark Rutland 2022-02-10 15:59 ` Frederic Weisbecker 2022-02-10 15:59 ` Frederic Weisbecker 2022-02-09 15:35 ` [PATCH v3 6/7] arm64: entry: centralize premeption decision Mark Rutland 2022-02-09 15:35 ` Mark Rutland 2022-02-09 18:10 ` Catalin Marinas 2022-02-09 18:10 ` Catalin Marinas 2022-02-10 9:19 ` Mark Rutland 2022-02-10 9:19 ` Mark Rutland 2022-02-09 15:35 ` Mark Rutland [this message] 2022-02-09 15:35 ` [PATCH v3 7/7] arm64: support PREEMPT_DYNAMIC Mark Rutland 2022-02-09 18:13 ` Catalin Marinas 2022-02-09 18:13 ` Catalin Marinas 2022-02-09 19:57 ` Frederic Weisbecker 2022-02-09 19:57 ` Frederic Weisbecker 2022-02-10 9:38 ` Mark Rutland 2022-02-10 9:38 ` Mark Rutland 2022-02-10 12:00 ` Mark Rutland 2022-02-10 12:00 ` Mark Rutland 2022-02-10 15:58 ` Frederic Weisbecker 2022-02-10 15:58 ` Frederic Weisbecker 2022-02-09 19:58 ` [PATCH v3 0/7] arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys Frederic Weisbecker 2022-02-09 19:58 ` Frederic Weisbecker 2022-02-10 9:29 ` Ard Biesheuvel 2022-02-10 9:29 ` Ard Biesheuvel
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