linux-kernel - [patch 1/5] tracehook: Provide TIF_NOTIFY

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Message-Id: <20190801143657.785902257@linutronix.de>
Date:   Thu, 01 Aug 2019 16:32:51 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julia Cartwright <julia@...com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, kvm@...r.kernel.org,
        Radim Krcmar <rkrcmar@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        John Stultz <john.stultz@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
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@...utronix.de>
Cc: Oleg Nesterov <oleg@...hat.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