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Subject[patch 1/5] tracehook: Provide TIF_NOTIFY_RESUME handling for KVM
TIF_NOTITY_RESUME is evaluated on return to user space along with other TIF
flags.

>From the kernels point of view a VMENTER is more or less equivalent to
return to user space which means that at least a subset of TIF flags needs
to be evaluated and handled.

Currently KVM handles only TIF_SIGPENDING and TIF_NEED_RESCHED, but
TIF_NOTIFY_RESUME is ignored. So pending task_work etc, is completely
ignored until the vCPU thread actually goes all the way back into
userspace/qemu.

Provide notify_resume_pending() and tracehook_handle_notify_resume() so
this can be handled similar to SIGPENDING.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Oleg Nesterov <oleg@redhat.com>
---
include/linux/tracehook.h | 15 +++++++++++++++
kernel/task_work.c | 19 +++++++++++++++++++
2 files changed, 34 insertions(+)

--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -163,6 +163,21 @@ static inline void set_notify_resume(str
#endif
}

+#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
+/**
+ * notify_resume_pending - Check whether current has TIF_NOTIFY_RESUME set
+ */
+static inline bool notify_resume_pending(void)
+{
+ return test_thread_flag(TIF_NOTIFY_RESUME);
+}
+
+void tracehook_handle_notify_resume(void);
+#else
+static inline bool notify_resume_pending(void) { return false; }
+static inline void tracehook_handle_notify_resume(void) { }
+#endif
+
/**
* tracehook_notify_resume - report when about to return to user mode
* @regs: user-mode registers of @current task
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -116,3 +116,22 @@ void task_work_run(void)
} while (work);
}
}
+
+#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
+/**
+ * tracehook_handle_notify_resume - Notify resume handling for virt
+ *
+ * Called with interrupts and preemption enabled from VMENTER/EXIT.
+ */
+void tracehook_handle_notify_resume(void)
+{
+ local_irq_disable();
+ while (test_and_clear_thread_flag(TIF_NOTIFY_RESUME)) {
+ local_irq_enable();
+ tracehook_notify_resume(NULL);
+ local_irq_disable();
+ }
+ local_irq_enable();
+}
+EXPORT_SYMBOL_GPL(tracehook_handle_notify_resume);
+#endif

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