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 287F0C433F5 for ; Mon, 14 Feb 2022 16:52:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1356747AbiBNQw4 (ORCPT ); Mon, 14 Feb 2022 11:52:56 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:33220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1356719AbiBNQwr (ORCPT ); Mon, 14 Feb 2022 11:52:47 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 823D465149 for ; Mon, 14 Feb 2022 08:52:38 -0800 (PST) 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 490A413D5; Mon, 14 Feb 2022 08:52:38 -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 4E7D93F70D; Mon, 14 Feb 2022 08:52:36 -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 v4 5/7] sched/preempt: add PREEMPT_DYNAMIC using static keys Date: Mon, 14 Feb 2022 16:52:14 +0000 Message-Id: <20220214165216.2231574-6-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220214165216.2231574-1-mark.rutland@arm.com> References: <20220214165216.2231574-1-mark.rutland@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Where an architecture selects HAVE_STATIC_CALL but not HAVE_STATIC_CALL_INLINE, each static call has an out-of-line trampoline which will either branch to a callee or return to the caller. On such architectures, a number of constraints can conspire to make those trampolines more complicated and potentially less useful than we'd like. For example: * Hardware and software control flow integrity schemes can require the addition of "landing pad" instructions (e.g. `BTI` for arm64), which will also be present at the "real" callee. * Limited branch ranges can require that trampolines generate or load an address into a register and perform an indirect branch (or at least have a slow path that does so). This loses some of the benefits of having a direct branch. * Interaction with SW CFI schemes can be complicated and fragile, e.g. requiring that we can recognise idiomatic codegen and remove indirections understand, at least until clang proves more helpful mechanisms for dealing with this. For PREEMPT_DYNAMIC, we don't need the full power of static calls, as we really only need to enable/disable specific preemption functions. We can achieve the same effect without a number of the pain points above by using static keys to fold early returns into the preemption functions themselves rather than in an out-of-line trampoline, effectively inlining the trampoline into the start of the function. For arm64, this results in good code generation. 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. | : | bti c | b // or `nop` | mov w0, #0x0 | ret | mrs x0, sp_el0 | ldr x0, [x0, #8] | cbnz x0, | paciasp | stp x29, x30, [sp, #-16]! | mov x29, sp | bl | 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 | mov w0, #0x1 | ldp x29, x30, [sp], #16 | autiasp | ret Any architecture which implements static keys should be able to use this to implement PREEMPT_DYNAMIC with similar cost to non-inlined static calls. Since this is likely to have greater overhead than (inlined) static calls, PREEMPT_DYNAMIC is only defaulted to enabled when HAVE_PREEMPT_DYNAMIC_CALL is selected. Signed-off-by: Mark Rutland Acked-by: Ard Biesheuvel Cc: Frederic Weisbecker Cc: Ingo Molnar Cc: Juri Lelli Cc: Peter Zijlstra Cc: Valentin Schneider --- arch/Kconfig | 36 ++++++++++++++++++++++-- arch/x86/Kconfig | 2 +- include/linux/entry-common.h | 10 +++++-- include/linux/kernel.h | 7 ++++- include/linux/sched.h | 10 ++++++- kernel/Kconfig.preempt | 3 +- kernel/entry/common.c | 11 ++++++++ kernel/sched/core.c | 54 ++++++++++++++++++++++++++++++++++-- 8 files changed, 122 insertions(+), 11 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index 601691f1570f..d544abd14c01 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1278,11 +1278,41 @@ config HAVE_STATIC_CALL_INLINE config HAVE_PREEMPT_DYNAMIC bool + +config HAVE_PREEMPT_DYNAMIC_CALL + bool depends on HAVE_STATIC_CALL + select HAVE_PREEMPT_DYNAMIC + help + An architecture should select this if it can handle the preemption + model being selected at boot time using static calls. + + Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a + preemption function will be patched directly. + + Where an architecture does not select HAVE_STATIC_CALL_INLINE, any + call to a preemption function will go through a trampoline, and the + trampoline will be patched. + + It is strongly advised to support inline static call to avoid any + overhead. + +config HAVE_PREEMPT_DYNAMIC_KEY + bool + depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO + select HAVE_PREEMPT_DYNAMIC help - Select this if the architecture support boot time preempt setting - on top of static calls. It is strongly advised to support inline - static call to avoid any overhead. + An architecture should select this if it can handle the preemption + model being selected at boot time using static keys. + + Each preemption function will be given an early return based on a + static key. This should have slightly lower overhead than non-inline + static calls, as this effectively inlines each trampoline into the + start of its callee. This may avoid redundant work, and may + integrate better with CFI schemes. + + This will have greater overhead than using inline static calls as + the call to the preemption function cannot be entirely elided. config ARCH_WANT_LD_ORPHAN_WARN bool diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 9f5bd41bf660..70f94094fd6f 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -246,7 +246,7 @@ config X86 select HAVE_STACK_VALIDATION if X86_64 select HAVE_STATIC_CALL select HAVE_STATIC_CALL_INLINE if HAVE_STACK_VALIDATION - select HAVE_PREEMPT_DYNAMIC + select HAVE_PREEMPT_DYNAMIC_CALL select HAVE_RSEQ select HAVE_SYSCALL_TRACEPOINTS select HAVE_UNSTABLE_SCHED_CLOCK diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h index dfd84c59b144..141952f4fee8 100644 --- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h @@ -456,13 +456,19 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs); */ void raw_irqentry_exit_cond_resched(void); #ifdef CONFIG_PREEMPT_DYNAMIC +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) #define irqentry_exit_cond_resched_dynamic_enabled raw_irqentry_exit_cond_resched #define irqentry_exit_cond_resched_dynamic_disabled NULL DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched); #define irqentry_exit_cond_resched() static_call(irqentry_exit_cond_resched)() -#else -#define irqentry_exit_cond_resched() raw_irqentry_exit_cond_resched() +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +void dynamic_irqentry_exit_cond_resched(void); +#define irqentry_exit_cond_resched() dynamic_irqentry_exit_cond_resched() #endif +#else /* CONFIG_PREEMPT_DYNAMIC */ +#define irqentry_exit_cond_resched() raw_irqentry_exit_cond_resched() +#endif /* CONFIG_PREEMPT_DYNAMIC */ /** * irqentry_exit - Handle return from exception that used irqentry_enter() diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 33f47a996513..a890428bcc1a 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -99,7 +99,7 @@ struct user; extern int __cond_resched(void); # define might_resched() __cond_resched() -#elif defined(CONFIG_PREEMPT_DYNAMIC) +#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) extern int __cond_resched(void); @@ -110,6 +110,11 @@ static __always_inline void might_resched(void) static_call_mod(might_resched)(); } +#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) + +extern int dynamic_might_resched(void); +# define might_resched() dynamic_might_resched() + #else # define might_resched() do { } while (0) diff --git a/include/linux/sched.h b/include/linux/sched.h index f5b2be39a78c..8b320fb54290 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2016,7 +2016,7 @@ static inline int test_tsk_need_resched(struct task_struct *tsk) #if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) extern int __cond_resched(void); -#ifdef CONFIG_PREEMPT_DYNAMIC +#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) DECLARE_STATIC_CALL(cond_resched, __cond_resched); @@ -2025,6 +2025,14 @@ static __always_inline int _cond_resched(void) return static_call_mod(cond_resched)(); } +#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +extern int dynamic_cond_resched(void); + +static __always_inline int _cond_resched(void) +{ + return dynamic_cond_resched(); +} + #else static inline int _cond_resched(void) diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index ce77f0265660..c2f1fd95a821 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -96,8 +96,9 @@ config PREEMPTION config PREEMPT_DYNAMIC bool "Preemption behaviour defined on boot" depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT + select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY select PREEMPT_BUILD - default y + default y if HAVE_PREEMPT_DYNAMIC_CALL help This option allows to define the preemption model on the kernel command line parameter and thus override the default preemption diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 1739ca79613b..b145249ad91a 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -3,6 +3,7 @@ #include #include #include +#include #include #include #include @@ -392,7 +393,17 @@ void raw_irqentry_exit_cond_resched(void) } } #ifdef CONFIG_PREEMPT_DYNAMIC +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched); +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +void dynamic_irqentry_exit_cond_resched(void) +{ + if (!static_key_unlikely(&sk_dynamic_irqentry_exit_cond_resched)) + return; + raw_irqentry_exit_cond_resched(); +} +#endif #endif noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3bf7f90d0ef7..4cca19d40636 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -14,6 +14,7 @@ #include #include +#include #include #include @@ -6482,21 +6483,31 @@ asmlinkage __visible void __sched notrace preempt_schedule(void) */ if (likely(!preemptible())) return; - preempt_schedule_common(); } NOKPROBE_SYMBOL(preempt_schedule); EXPORT_SYMBOL(preempt_schedule); #ifdef CONFIG_PREEMPT_DYNAMIC +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) #ifndef preempt_schedule_dynamic_enabled #define preempt_schedule_dynamic_enabled preempt_schedule #define preempt_schedule_dynamic_disabled NULL #endif DEFINE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled); EXPORT_STATIC_CALL_TRAMP(preempt_schedule); +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule); +void __sched notrace dynamic_preempt_schedule(void) +{ + if (!static_branch_unlikely(&sk_dynamic_preempt_schedule)) + return; + preempt_schedule(); +} +NOKPROBE_SYMBOL(dynamic_preempt_schedule); +EXPORT_SYMBOL(dynamic_preempt_schedule); +#endif #endif - /** * preempt_schedule_notrace - preempt_schedule called by tracing @@ -6551,12 +6562,24 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void) EXPORT_SYMBOL_GPL(preempt_schedule_notrace); #ifdef CONFIG_PREEMPT_DYNAMIC +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) #ifndef preempt_schedule_notrace_dynamic_enabled #define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace #define preempt_schedule_notrace_dynamic_disabled NULL #endif DEFINE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled); EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace); +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule_notrace); +void __sched notrace dynamic_preempt_schedule_notrace(void) +{ + if (!static_branch_unlikely(&sk_dynamic_preempt_schedule_notrace)) + return; + preempt_schedule_notrace(); +} +NOKPROBE_SYMBOL(dynamic_preempt_schedule_notrace); +EXPORT_SYMBOL(dynamic_preempt_schedule_notrace); +#endif #endif #endif /* CONFIG_PREEMPTION */ @@ -8066,6 +8089,7 @@ EXPORT_SYMBOL(__cond_resched); #endif #ifdef CONFIG_PREEMPT_DYNAMIC +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) #define cond_resched_dynamic_enabled __cond_resched #define cond_resched_dynamic_disabled ((void *)&__static_call_return0) DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched); @@ -8075,6 +8099,25 @@ EXPORT_STATIC_CALL_TRAMP(cond_resched); #define might_resched_dynamic_disabled ((void *)&__static_call_return0) DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched); EXPORT_STATIC_CALL_TRAMP(might_resched); +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched); +int __sched dynamic_cond_resched(void) +{ + if (!static_branch_unlikely(&sk_dynamic_cond_resched)) + return 0; + return __cond_resched(); +} +EXPORT_SYMBOL(dynamic_cond_resched); + +static DEFINE_STATIC_KEY_FALSE(sk_dynamic_might_resched); +int __sched dynamic_might_resched(void) +{ + if (!static_branch_unlikely(&sk_dynamic_might_resched)) + return 0; + return __cond_resched(); +} +EXPORT_SYMBOL(dynamic_might_resched); +#endif #endif /* @@ -8198,8 +8241,15 @@ int sched_dynamic_mode(const char *str) return -EINVAL; } +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) #define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled) #define preempt_dynamic_disable(f) static_call_update(f, f##_dynamic_disabled) +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) +#define preempt_dynamic_enable(f) static_key_enable(&sk_dynamic_##f.key) +#define preempt_dynamic_disable(f) static_key_disable(&sk_dynamic_##f.key) +#else +#error "Unsupported PREEMPT_DYNAMIC mechanism" +#endif void sched_dynamic_update(int mode) { -- 2.30.2