Commit 7c68af6e authored by Avi Kivity's avatar Avi Kivity Committed by H. Peter Anvin
Browse files

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: default avatarAvi Kivity <avi@redhat.com>
LKML-Reference: <1253342422-13811-1-git-send-email-avi@redhat.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 817b33d3

arch/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -83,6 +83,13 @@ config KRETPROBES 
	def_bool y

	depends on KPROBES && HAVE_KRETPROBES



config USER_RETURN_NOTIFIER

	bool

	depends on HAVE_USER_RETURN_NOTIFIER

	help

	  Provide a kernel-internal notification when a cpu is about to

	  switch to user mode.



config HAVE_IOREMAP_PROT

	bool
@@ -126,4 +133,7 @@ config HAVE_DMA_API_DEBUG 
config HAVE_DEFAULT_NO_SPIN_MUTEXES

	bool



config HAVE_USER_RETURN_NOTIFIER

	bool



source "kernel/gcov/Kconfig"

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -50,6 +50,7 @@ config X86 
	select HAVE_KERNEL_BZIP2

	select HAVE_KERNEL_LZMA

	select HAVE_ARCH_KMEMCHECK

	select HAVE_USER_RETURN_NOTIFIER



config OUTPUT_FORMAT

	string

arch/x86/include/asm/thread_info.h

+5 −2
Original line number Diff line number Diff line
@@ -83,6 +83,7 @@ struct thread_info { 
#define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */

#define TIF_SECCOMP		8	/* secure computing */

#define TIF_MCE_NOTIFY		10	/* notify userspace of an MCE */

#define TIF_USER_RETURN_NOTIFY	11	/* notify kernel of userspace return */

#define TIF_NOTSC		16	/* TSC is not accessible in userland */

#define TIF_IA32		17	/* 32bit process */

#define TIF_FORK		18	/* ret_from_fork */
@@ -107,6 +108,7 @@ struct thread_info { 
#define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)

#define _TIF_SECCOMP		(1 << TIF_SECCOMP)

#define _TIF_MCE_NOTIFY		(1 << TIF_MCE_NOTIFY)

#define _TIF_USER_RETURN_NOTIFY	(1 << TIF_USER_RETURN_NOTIFY)

#define _TIF_NOTSC		(1 << TIF_NOTSC)

#define _TIF_IA32		(1 << TIF_IA32)

#define _TIF_FORK		(1 << TIF_FORK)
@@ -142,13 +144,14 @@ struct thread_info { 


/* Only used for 64 bit */

#define _TIF_DO_NOTIFY_MASK						\

	(_TIF_SIGPENDING|_TIF_MCE_NOTIFY|_TIF_NOTIFY_RESUME)

	(_TIF_SIGPENDING | _TIF_MCE_NOTIFY | _TIF_NOTIFY_RESUME |	\

	 _TIF_USER_RETURN_NOTIFY)



/* flags to check in __switch_to() */

#define _TIF_WORK_CTXSW							\

	(_TIF_IO_BITMAP|_TIF_DEBUGCTLMSR|_TIF_DS_AREA_MSR|_TIF_NOTSC)



#define _TIF_WORK_CTXSW_PREV _TIF_WORK_CTXSW

#define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY)

#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW|_TIF_DEBUG)



#define PREEMPT_ACTIVE		0x10000000

arch/x86/kernel/process.c

+2 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
#include <linux/pm.h>

#include <linux/clockchips.h>

#include <linux/random.h>

#include <linux/user-return-notifier.h>

#include <trace/events/power.h>

#include <asm/system.h>

#include <asm/apic.h>
@@ -224,6 +225,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p, 
		 */

		memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);

	}

	propagate_user_return_notify(prev_p, next_p);

}



int sys_fork(struct pt_regs *regs)

arch/x86/kernel/signal.c

+3 −0
Original line number Diff line number Diff line
@@ -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);

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