From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4842C433F5 for ; Fri, 4 Feb 2022 15:06:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1359595AbiBDPGg (ORCPT ); Fri, 4 Feb 2022 10:06:36 -0500 Received: from foss.arm.com ([217.140.110.172]:50330 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1359585AbiBDPG3 (ORCPT ); Fri, 4 Feb 2022 10:06:29 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 853DC1477; Fri, 4 Feb 2022 07:06:29 -0800 (PST) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 28BA63F774; Fri, 4 Feb 2022 07:06:27 -0800 (PST) From: Mark Rutland 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 v2 7/7] arm64: support PREEMPT_DYNAMIC Date: Fri, 4 Feb 2022 15:05:57 +0000 Message-Id: <20220204150557.434610-8-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220204150557.434610-1-mark.rutland@arm.com> References: <20220204150557.434610-1-mark.rutland@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 (with the first `B` being replaced with a `NOP` when the function is disabled): | : | bti c | b | mov w0, #0x0 // #0 | ret | mrs x0, sp_el0 | ldr x0, [x0, #8] | cbnz x0, | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl | mov w0, #0x1 // #1 | 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 // #0 | ret | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl | mov w0, #0x1 // #1 | 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 Cc: Ard Biesheuvel Cc: Catalin Marinas Cc: Frederic Weisbecker Cc: Ingo Molnar Cc: Joey Gouly Cc: Juri Lelli Cc: Peter Zijlstra Cc: Valentin Schneider Cc: Will Deacon --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/preempt.h | 16 ++++++++++++++-- arch/arm64/kernel/entry-common.c | 10 +++++++++- 3 files changed, 24 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..73623f719d7e 100644 --- a/arch/arm64/include/asm/preempt.h +++ b/arch/arm64/include/asm/preempt.h @@ -80,10 +80,22 @@ static inline bool should_resched(int preempt_offset) } #ifdef CONFIG_PREEMPTION +#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 + void preempt_schedule(void); -#define __preempt_schedule() preempt_schedule() +#define __preempt_schedule() preempt_schedule() void preempt_schedule_notrace(void); -#define __preempt_schedule_notrace() preempt_schedule_notrace() +#define __preempt_schedule_notrace() preempt_schedule_notrace() + +#endif #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