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authorAvi Kivity <avi@redhat.com>2009-09-19 09:40:22 +0300
committerH. Peter Anvin <hpa@zytor.com>2009-10-01 12:12:18 -0700
commit7c68af6e32c73992bad24107311f3433c89016e2 (patch)
tree9046ac5339f944e8ddccd34be226790b953dda61 /kernel/user-return-notifier.c
parent817b33d38f81c8736d39283c35c886ae4668f1af (diff)
downloadlinux-sh-7c68af6e32c73992bad24107311f3433c89016e2.tar.gz
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 <avi@redhat.com> LKML-Reference: <1253342422-13811-1-git-send-email-avi@redhat.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'kernel/user-return-notifier.c')
-rw-r--r--kernel/user-return-notifier.c46
1 files changed, 46 insertions, 0 deletions
diff --git a/kernel/user-return-notifier.c b/kernel/user-return-notifier.c
new file mode 100644
index 000000000000..530ccb816513
--- /dev/null
+++ b/kernel/user-return-notifier.c
@@ -0,0 +1,46 @@
+
+#include <linux/user-return-notifier.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+
+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();
+}