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Subject[PATCH 1/4] core, x86: Add user return notifiers
Date
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.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/Kconfig | 10 ++++++++++
arch/x86/Kconfig | 1 +
arch/x86/include/asm/thread_info.h | 7 +++++--
arch/x86/kernel/process.c | 2 ++
arch/x86/kernel/signal.c | 3 +++
kernel/Makefile | 1 +
6 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 99193b1..2275b46 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -70,6 +70,13 @@ 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

@@ -113,4 +120,7 @@ config HAVE_DMA_API_DEBUG
config HAVE_DEFAULT_NO_SPIN_MUTEXES
bool

+config HAVE_USER_RETURN_NOTIFIER
+ bool
+
source "kernel/gcov/Kconfig"
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 13ffa5d..5fc4fae 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index fad7d40..a8f46de 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -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)
@@ -141,13 +143,14 @@ 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
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 071166a..7ea6972 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -9,6 +9,7 @@
#include <linux/pm.h>
#include <linux/clockchips.h>
#include <linux/random.h>
+#include <linux/user-return-notifier.h>
#include <trace/power.h>
#include <asm/system.h>
#include <asm/apic.h>
@@ -227,6 +228,7 @@ 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)
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 4c57875..bc0db10 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -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>
@@ -870,6 +871,8 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
}
+ if (thread_info_flags & _TIF_USER_RETURN_NOTIFY)
+ fire_user_return_notifiers();

#ifdef CONFIG_X86_32
clear_thread_flag(TIF_IRET);
diff --git a/kernel/Makefile b/kernel/Makefile
index 2093a69..11c5de5 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -100,6 +100,7 @@ obj-$(CONFIG_RING_BUFFER) += trace/
obj-$(CONFIG_SMP) += sched_cpupri.o
obj-$(CONFIG_SLOW_WORK) += slow-work.o
obj-$(CONFIG_PERF_COUNTERS) += perf_counter.o
+obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o

ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
# According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
--
1.6.4.1


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