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McKenney" , Chris Metcalf , Christopher Lameter , Russell King - ARM Linux , Mark Rutland , Steven Rostedt , Mathieu Desnoyers , Catalin Marinas , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] smp: introduce kick_active_cpus_sync() Message-ID: <20180401111108.mudkiewzn33sifvk@yury-thinkpad> References: <20180325175004.28162-1-ynorov@caviumnetworks.com> <20180325175004.28162-3-ynorov@caviumnetworks.com> <20180327102116.GA2464@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180327102116.GA2464@arm.com> User-Agent: NeoMutt/20170609 (1.8.3) X-Originating-IP: [50.233.148.156] X-ClientProxiedBy: HE1PR06CA0153.eurprd06.prod.outlook.com (10.170.251.40) To BN6PR07MB2898.namprd07.prod.outlook.com (10.173.28.144) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 99217bb9-48dd-4732-1945-08d597c14f30 X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(5600026)(4604075)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7153060)(7193020);SRVR:BN6PR07MB2898; 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Delaying synchronization helps to > > save power if CPU is in idle state and decrease latency for real-time tasks. > > > > This patch introduces kick_active_cpus_sync() and uses it in mm/slab and arm64 > > code to delay syncronization. > > > > For task isolation (https://lkml.org/lkml/2017/11/3/589), IPI to the CPU running > > isolated task would be fatal, as it breaks isolation. The approach with delaying > > of synchronization work helps to maintain isolated state. > > > > I've tested it with test from task isolation series on ThunderX2 for more than > > 10 hours (10k giga-ticks) without breaking isolation. > > > > Signed-off-by: Yury Norov > > --- > > arch/arm64/kernel/insn.c | 2 +- > > include/linux/smp.h | 2 ++ > > kernel/smp.c | 24 ++++++++++++++++++++++++ > > mm/slab.c | 2 +- > > 4 files changed, 28 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c > > index 2718a77da165..9d7c492e920e 100644 > > --- a/arch/arm64/kernel/insn.c > > +++ b/arch/arm64/kernel/insn.c > > @@ -291,7 +291,7 @@ int __kprobes aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt) > > * synchronization. > > */ > > ret = aarch64_insn_patch_text_nosync(addrs[0], insns[0]); > > - kick_all_cpus_sync(); > > + kick_active_cpus_sync(); > > return ret; > > } > > } > > I think this means that runtime modifications to the kernel text might not > be picked up by CPUs coming out of idle. Shouldn't we add an ISB on that > path to avoid executing stale instructions? > > Will commit 153ae9d5667e7baab4d48c48e8ec30fbcbd86f1e Author: Yury Norov Date: Sat Mar 31 15:05:23 2018 +0300 Hi Will, Paul, On my system there are 3 paths that go thru rcu_dynticks_eqs_exit(), and so require isb(). First path starts at gic_handle_irq() on secondary_start_kernel stack. gic_handle_irq() already issues isb(), and so we can do nothing. Second path starts at el0_svc entry; and third path is the exit from do_idle() on secondary_start_kernel stack. For do_idle() path there is arch_cpu_idle_exit() hook that is not used by arm64 at now, so I picked it. And for el0_svc, I've introduced isb_if_eqs macro and call it at the beginning of el0_svc_naked. I've tested it on ThunderX2 machine, and it works for me. Below is my call traces and patch for them. If you OK with it, I think I'm ready to submit v2 (but maybe split this patch for better readability). Yury [ 585.412095] Call trace: [ 585.412097] [] dump_backtrace+0x0/0x380 [ 585.412099] [] show_stack+0x14/0x20 [ 585.412101] [] dump_stack+0x98/0xbc [ 585.412104] [] rcu_dynticks_eqs_exit+0x68/0x70 [ 585.412105] [] rcu_irq_enter+0x48/0x50 [ 585.412106] [] irq_enter+0xc/0x70 [ 585.412108] [] __handle_domain_irq+0x3c/0x120 [ 585.412109] [] gic_handle_irq+0xc4/0x180 [ 585.412110] Exception stack(0xfffffc001130fe20 to 0xfffffc001130ff60) [ 585.412112] fe20: 00000000000000a0 0000000000000000 0000000000000001 0000000000000000 [ 585.412113] fe40: 0000028f6f0b0000 0000000000000020 0013cd6f53963b31 0000000000000000 [ 585.412144] fe60: 0000000000000002 fffffc001130fed0 0000000000000b80 0000000000003400 [ 585.412146] fe80: 0000000000000000 0000000000000001 0000000000000000 00000000000001db [ 585.412147] fea0: fffffc0008247a78 000003ff86dc61f8 0000000000000014 fffffc0008fc0000 [ 585.412149] fec0: fffffc00090143e8 fffffc0009014000 fffffc0008fc94a0 0000000000000000 [ 585.412150] fee0: 0000000000000000 fffffe8f46bb1700 0000000000000000 0000000000000000 [ 585.412152] ff00: 0000000000000000 fffffc001130ff60 fffffc0008085034 fffffc001130ff60 [ 585.412153] ff20: fffffc0008085038 0000000000400149 fffffc0009014000 fffffc0008fc94a0 [ 585.412155] ff40: ffffffffffffffff 0000000000000000 fffffc001130ff60 fffffc0008085038 [ 585.412156] [] el1_irq+0xb0/0x124 [ 585.412158] [] arch_cpu_idle+0x10/0x18 [ 585.412159] [] do_idle+0x10c/0x1d8 [ 585.412160] [] cpu_startup_entry+0x24/0x28 [ 585.412162] [] secondary_start_kernel+0x15c/0x1a0 [ 585.412164] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.14.0-isolation-160735-g59b71c1-dirty #18 [ 585.412058] Call trace: [ 585.412060] [] dump_backtrace+0x0/0x380 [ 585.412062] [] show_stack+0x14/0x20 [ 585.412064] [] dump_stack+0x98/0xbc [ 585.412066] [] rcu_dynticks_eqs_exit+0x68/0x70 [ 585.412068] [] rcu_eqs_exit.isra.23+0x64/0x80 [ 585.412069] [] rcu_user_exit+0xc/0x18 [ 585.412071] [] __context_tracking_exit.part.2+0x74/0x98 [ 585.412072] [] context_tracking_exit.part.3+0x40/0x50 [ 585.412074] [] context_tracking_user_exit+0x30/0x38 [ 585.412075] Exception stack(0xfffffc00385afec0 to 0xfffffc00385b0000) [ 585.412076] fec0: 00000000000000b1 000002aacd702420 0000000000000200 00000000000001f4 [ 585.412078] fee0: 0000000000000000 0000000000000008 000002aabec9af17 ffffffffffffffff [ 585.412079] ff00: 0000000000000016 ffffffffffffffff 000003ffe7619470 0000000000000057 [ 585.412081] ff20: a3d70a3d70a3d70b 000000000000016d 2ce33e6c02ce33e7 00000000000001db [ 585.412082] ff40: 000002aabec7d260 000003ff86dc61f8 0000000000000014 00000000000001f4 [ 585.412083] ff60: 0000000000000000 000002aabecab000 000002aacd6e2830 0000000000000001 [ 585.412085] ff80: 000002aacd6e2830 000002aabec58380 0000000000000054 000002aabebccf50 [ 585.412086] ffa0: 0000000000000054 000003ffe7619540 000002aabebcf538 000003ffe7619540 [ 585.412088] ffc0: 000003ff86dc6410 0000000060000000 00000000000000b1 0000000000000016 [ 585.412089] ffe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 585.412091] [] el0_svc_naked+0xc/0x3c [ 585.446067] CPU: 68 PID: 0 Comm: swapper/68 Not tainted 4.14.0-isolation-160735-g59b71c1-dirty #18 [ 585.412038] Call trace: [ 585.412041] [] dump_backtrace+0x0/0x380 [ 585.412042] [] show_stack+0x14/0x20 [ 585.412045] [] dump_stack+0x98/0xbc [ 585.412047] [] rcu_dynticks_eqs_exit+0x68/0x70 [ 585.412049] [] rcu_eqs_exit.isra.23+0x64/0x80 [ 585.412050] [] rcu_idle_exit+0x18/0x28 [ 585.412052] [] do_idle+0x118/0x1d8 [ 585.412053] [] cpu_startup_entry+0x24/0x28 [ 585.412055] [] secondary_start_kernel+0x15c/0x1a0 [ 585.412057] CPU: 22 PID: 4315 Comm: nginx Not tainted 4.14.0-isolation-160735-g59b71c1-dirty #18 diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index e1c59d4008a8..efa5060a2f1c 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -35,22 +35,29 @@ #include /* - * Context tracking subsystem. Used to instrument transitions - * between user and kernel mode. + * Save/restore needed during syscalls. Restore syscall arguments from + * the values already saved on stack during kernel_entry. */ - .macro ct_user_exit, syscall = 0 -#ifdef CONFIG_CONTEXT_TRACKING - bl context_tracking_user_exit - .if \syscall == 1 - /* - * Save/restore needed during syscalls. Restore syscall arguments from - * the values already saved on stack during kernel_entry. - */ + .macro __restore_syscall_args ldp x0, x1, [sp] ldp x2, x3, [sp, #S_X2] ldp x4, x5, [sp, #S_X4] ldp x6, x7, [sp, #S_X6] - .endif + .endm + + .macro el0_svc_restore_syscall_args +#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_CONTEXT_TRACKING) + __restore_syscall_args +#endif + .endm + +/* + * Context tracking subsystem. Used to instrument transitions + * between user and kernel mode. + */ + .macro ct_user_exit +#ifdef CONFIG_CONTEXT_TRACKING + bl context_tracking_user_exit #endif .endm @@ -433,6 +440,20 @@ __bad_stack: ASM_BUG() .endm +/* + * Flush I-cache if CPU is in extended quiescent state + */ + .macro isb_if_eqs +#ifndef CONFIG_TINY_RCU + bl rcu_is_watching + tst w0, #0xff + b.ne 1f + /* Pairs with aarch64_insn_patch_text for EQS CPUs. */ + isb +1: +#endif + .endm + el0_sync_invalid: inv_entry 0, BAD_SYNC ENDPROC(el0_sync_invalid) @@ -840,8 +861,10 @@ el0_svc: mov wsc_nr, #__NR_syscalls el0_svc_naked: // compat entry point stp x0, xscno, [sp, #S_ORIG_X0] // save the original x0 and syscall number + isb_if_eqs enable_dbg_and_irq - ct_user_exit 1 + ct_user_exit + el0_svc_restore_syscall_args ldr x16, [tsk, #TSK_TI_FLAGS] // check for syscall hooks tst x16, #_TIF_SYSCALL_WORK @@ -874,10 +897,7 @@ __sys_trace: mov x1, sp // pointer to regs cmp wscno, wsc_nr // check upper syscall limit b.hs __ni_sys_trace - ldp x0, x1, [sp] // restore the syscall args - ldp x2, x3, [sp, #S_X2] - ldp x4, x5, [sp, #S_X4] - ldp x6, x7, [sp, #S_X6] + __restore_syscall_args ldr x16, [stbl, xscno, lsl #3] // address in the syscall table blr x16 // call sys_* routine diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 2dc0f8482210..f11afd2aa33a 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -88,6 +88,12 @@ void arch_cpu_idle(void) trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id()); } +void arch_cpu_idle_exit(void) +{ + if (!rcu_is_watching()) + isb(); +} + #ifdef CONFIG_HOTPLUG_CPU void arch_cpu_idle_dead(void) {