From 7c68af6e32c73992bad24107311f3433c89016e2 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Sat, 19 Sep 2009 09:40:22 +0300 Subject: core, x86: Add user return notifiers Add a general per-cpu notifier that is called whenever the kernel is about to return to userspace. The notifier uses a thread_info flag and existing checks, so there is no impact on user return or context switch fast paths. This will be used initially to speed up KVM task switching by lazily updating MSRs. Signed-off-by: Avi Kivity LKML-Reference: <1253342422-13811-1-git-send-email-avi@redhat.com> Signed-off-by: H. Peter Anvin --- kernel/user-return-notifier.c | 46 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 46 insertions(+) create mode 100644 kernel/user-return-notifier.c (limited to 'kernel') diff --git a/kernel/user-return-notifier.c b/kernel/user-return-notifier.c new file mode 100644 index 00000000000..530ccb81651 --- /dev/null +++ b/kernel/user-return-notifier.c @@ -0,0 +1,46 @@ + +#include +#include +#include +#include + +static DEFINE_PER_CPU(struct hlist_head, return_notifier_list); + +#define URN_LIST_HEAD per_cpu(return_notifier_list, raw_smp_processor_id()) + +/* + * Request a notification when the current cpu returns to userspace. Must be + * called in atomic context. The notifier will also be called in atomic + * context. + */ +void user_return_notifier_register(struct user_return_notifier *urn) +{ + set_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY); + hlist_add_head(&urn->link, &URN_LIST_HEAD); +} +EXPORT_SYMBOL_GPL(user_return_notifier_register); + +/* + * Removes a registered user return notifier. Must be called from atomic + * context, and from the same cpu registration occured in. + */ +void user_return_notifier_unregister(struct user_return_notifier *urn) +{ + hlist_del(&urn->link); + if (hlist_empty(&URN_LIST_HEAD)) + clear_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY); +} +EXPORT_SYMBOL_GPL(user_return_notifier_unregister); + +/* Calls registered user return notifiers */ +void fire_user_return_notifiers(void) +{ + struct user_return_notifier *urn; + struct hlist_node *tmp1, *tmp2; + struct hlist_head *head; + + head = &get_cpu_var(return_notifier_list); + hlist_for_each_entry_safe(urn, tmp1, tmp2, head, link) + urn->on_user_return(urn); + put_cpu_var(); +} -- cgit v1.2.3-70-g09d2 From 7a041097518a120f92af631a83db4d41e07ee51b Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Sun, 25 Oct 2009 14:24:45 +0200 Subject: x86: Fix user return notifier build When CONFIG_USER_RETURN_NOTIFIER is set, we need to link kernel/user-return-notifier.o. Signed-off-by: Avi Kivity LKML-Reference: <1256473485-23109-1-git-send-email-avi@redhat.com> Signed-off-by: Ingo Molnar --- kernel/Makefile | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel') diff --git a/kernel/Makefile b/kernel/Makefile index b8d4cd8ac0b..0ae57a83d48 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -95,6 +95,7 @@ obj-$(CONFIG_RING_BUFFER) += trace/ obj-$(CONFIG_SMP) += sched_cpupri.o obj-$(CONFIG_SLOW_WORK) += slow-work.o obj-$(CONFIG_PERF_EVENTS) += perf_event.o +obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y) # According to Alan Modra , the -fno-omit-frame-pointer is -- cgit v1.2.3-70-g09d2 From 3c912b6edaac56cb451e7571c95c15cbb6bd0c81 Mon Sep 17 00:00:00 2001 From: Stephen Rothwell Date: Mon, 2 Nov 2009 16:17:22 +1100 Subject: x86: Fix user return notifier put_cpu_var() invocation Today's linux-next build (x86_64 allmodconfig) failed like this: kernel/user-return-notifier.c: In function 'fire_user_return_notifiers': kernel/user-return-notifier.c:45: error: expected expression before ')' token Introduced by commit 7c68af6e32c73992bad24107311f3433c89016e2 ("core, x86: Add user return notifiers") from the tip and kvm trees but revealed by commit e0fdb0e050eae331046385643618f12452aa7e73 ("percpu: add __percpu for sparse") from the percpu tree. Before that percpu tree commit, "put_cpu_var()" would compile without error (even though it really needs a parameter). Signed-off-by: Stephen Rothwell Cc: Avi Kivity Cc: Peter Zijlstra Cc: Tejun Heo Cc: Rusty Russell Cc: Christoph Lameter LKML-Reference: <20091102161722.eea4358d.sfr@canb.auug.org.au> Signed-off-by: Ingo Molnar --- kernel/user-return-notifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/user-return-notifier.c b/kernel/user-return-notifier.c index 530ccb81651..03e2d6fd9b1 100644 --- a/kernel/user-return-notifier.c +++ b/kernel/user-return-notifier.c @@ -42,5 +42,5 @@ void fire_user_return_notifiers(void) head = &get_cpu_var(return_notifier_list); hlist_for_each_entry_safe(urn, tmp1, tmp2, head, link) urn->on_user_return(urn); - put_cpu_var(); + put_cpu_var(return_notifier_list); } -- cgit v1.2.3-70-g09d2 From 8e7cac79808b62f242069a6ac88d364d35621371 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Sun, 29 Nov 2009 16:34:48 +0200 Subject: core: Fix user return notifier on fork() fork() clones all thread_info flags, including TIF_USER_RETURN_NOTIFY; if the new task is first scheduled on a cpu which doesn't have user return notifiers set, this causes user return notifiers to trigger without any way of clearing itself. This is easy to trigger with a forky workload on the host in parallel with kvm, resulting in a cpu in an endless loop on the verge of returning to userspace. Fix by dropping the TIF_USER_RETURN_NOTIFY immediately after fork. Signed-off-by: Avi Kivity LKML-Reference: <1259505288-16559-1-git-send-email-avi@redhat.com> Signed-off-by: Ingo Molnar --- include/linux/user-return-notifier.h | 7 +++++++ kernel/fork.c | 2 ++ 2 files changed, 9 insertions(+) (limited to 'kernel') diff --git a/include/linux/user-return-notifier.h b/include/linux/user-return-notifier.h index b6ac056291d..9c4a445bb43 100644 --- a/include/linux/user-return-notifier.h +++ b/include/linux/user-return-notifier.h @@ -26,6 +26,11 @@ static inline void propagate_user_return_notify(struct task_struct *prev, void fire_user_return_notifiers(void); +static inline void clear_user_return_notifier(struct task_struct *p) +{ + clear_tsk_thread_flag(p, TIF_USER_RETURN_NOTIFY); +} + #else struct user_return_notifier {}; @@ -37,6 +42,8 @@ static inline void propagate_user_return_notify(struct task_struct *prev, static inline void fire_user_return_notifiers(void) {} +static inline void clear_user_return_notifier(struct task_struct *p) {} + #endif #endif diff --git a/kernel/fork.c b/kernel/fork.c index 266c6af6ef1..1b7512d5a64 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -64,6 +64,7 @@ #include #include #include +#include #include #include @@ -249,6 +250,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig) goto out; setup_thread_stack(tsk, orig); + clear_user_return_notifier(tsk); stackend = end_of_stack(tsk); *stackend = STACK_END_MAGIC; /* for overflow detection */ -- cgit v1.2.3-70-g09d2