From df156f90a0f90649dd38b7667901ef85478f3d2b Mon Sep 17 00:00:00 2001 From: Igor Mammedov Date: Tue, 7 Feb 2012 15:52:44 +0100 Subject: [PATCH] x86: Introduce x86_cpuinit.early_percpu_clock_init hook When kvm guest uses kvmclock, it may hang on vcpu hot-plug. This is caused by an overflow in pvclock_get_nsec_offset, u64 delta = tsc - shadow->tsc_timestamp; which in turn is caused by an undefined values from percpu hv_clock that hasn't been initialized yet. Uninitialized clock on being booted cpu is accessed from start_secondary -> smp_callin -> smp_store_cpu_info -> identify_secondary_cpu -> mtrr_ap_init -> mtrr_restore -> stop_machine_from_inactive_cpu -> queue_stop_cpus_work ... -> sched_clock -> kvm_clock_read which is well before x86_cpuinit.setup_percpu_clockev call in start_secondary, where percpu clock is initialized. This patch introduces a hook that allows to setup/initialize per_cpu clock early and avoid overflow due to reading - undefined values - old values if cpu was offlined and then onlined again Another possible early user of this clock source is ftrace that accesses it to get timestamps for ring buffer entries. So if mtrr_ap_init is moved from identify_secondary_cpu to past x86_cpuinit.setup_percpu_clockev in start_secondary, ftrace may cause the same overflow/hang on cpu hot-plug anyway. More complete description of the problem: https://lkml.org/lkml/2012/2/2/101 Credits to Marcelo Tosatti for hook idea. Acked-by: Thomas Gleixner Signed-off-by: Igor Mammedov Signed-off-by: Marcelo Tosatti Signed-off-by: Avi Kivity --- arch/x86/include/asm/x86_init.h | 2 ++ arch/x86/kernel/kvmclock.c | 4 +--- arch/x86/kernel/smpboot.c | 1 + arch/x86/kernel/x86_init.c | 1 + 4 files changed, 5 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h index 517d476..5d0afac 100644 --- a/arch/x86/include/asm/x86_init.h +++ b/arch/x86/include/asm/x86_init.h @@ -145,9 +145,11 @@ struct x86_init_ops { /** * struct x86_cpuinit_ops - platform specific cpu hotplug setups * @setup_percpu_clockev: set up the per cpu clock event device + * @early_percpu_clock_init: early init of the per cpu clock event device */ struct x86_cpuinit_ops { void (*setup_percpu_clockev)(void); + void (*early_percpu_clock_init)(void); void (*fixup_cpu_id)(struct cpuinfo_x86 *c, int node); }; diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index 44842d7..ca4e735 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -144,8 +144,6 @@ static void __cpuinit kvm_setup_secondary_clock(void) * we shouldn't fail. */ WARN_ON(kvm_register_clock("secondary cpu clock")); - /* ok, done with our trickery, call native */ - setup_secondary_APIC_clock(); } #endif @@ -194,7 +192,7 @@ void __init kvmclock_init(void) x86_platform.get_wallclock = kvm_get_wallclock; x86_platform.set_wallclock = kvm_set_wallclock; #ifdef CONFIG_X86_LOCAL_APIC - x86_cpuinit.setup_percpu_clockev = + x86_cpuinit.early_percpu_clock_init = kvm_setup_secondary_clock; #endif machine_ops.shutdown = kvm_shutdown; diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 66d250c..a05d6fd 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -255,6 +255,7 @@ notrace static void __cpuinit start_secondary(void *unused) * most necessary things. */ cpu_init(); + x86_cpuinit.early_percpu_clock_init(); preempt_disable(); smp_callin(); diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c index 947a06c..6f2ec53 100644 --- a/arch/x86/kernel/x86_init.c +++ b/arch/x86/kernel/x86_init.c @@ -91,6 +91,7 @@ struct x86_init_ops x86_init __initdata = { }; struct x86_cpuinit_ops x86_cpuinit __cpuinitdata = { + .early_percpu_clock_init = x86_init_noop, .setup_percpu_clockev = setup_secondary_APIC_clock, .fixup_cpu_id = x86_default_fixup_cpu_id, }; -- 2.7.4