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>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8da9374..1df175d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -50,6 +50,7 @@
select HAVE_KERNEL_BZIP2
select HAVE_KERNEL_LZMA
select HAVE_ARCH_KMEMCHECK
+ select HAVE_USER_RETURN_NOTIFIER
config OUTPUT_FORMAT
string