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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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3
arch/x86/kernel/signal.c
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@@ -19,6 +19,7 @@
#include <linux/stddef.h>
#include <linux/personality.h>
#include <linux/uaccess.h>
#include <linux/user-return-notifier.h>
#include <asm/processor.h>
#include <asm/ucontext.h>
@@ -872,6 +873,8 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
if (thread_info_flags & _TIF_USER_RETURN_NOTIFY)
fire_user_return_notifiers();
#ifdef CONFIG_X86_32
clear_thread_flag(TIF_IRET);