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core, x86: Add user return notifiers

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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>
This commit is contained in:
Avi Kivity
2009-09-19 09:40:22 +03:00
committed by H. Peter Anvin
parent 817b33d38f
commit 7c68af6e32
7 changed files with 109 additions and 2 deletions
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46
kernel/user-return-notifier.c Normal file
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#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();
}