[PATCH 4/4] um: allow PM with suspend-to-idle

[Johannes Berg]

From: Johannes Berg <johannes.berg at intel.com>

In order to be able to experiment with suspend in UML,
add the minimal work to be able to suspend (s2idle) an
instance of UML, and be able to wake it back up from
that state with the USR1 signal sent to the main UML
process.

Signed-off-by: Johannes Berg <johannes.berg at intel.com>
---
 arch/um/Kconfig                    |  5 +++++
 arch/um/include/shared/kern_util.h |  2 ++
 arch/um/include/shared/os.h        |  1 +
 arch/um/kernel/um_arch.c           | 25 +++++++++++++++++++++++++
 arch/um/os-Linux/signal.c          | 14 +++++++++++++-
 5 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index eb51fec75948..daee3bf35942 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -207,3 +207,8 @@ config UML_TIME_TRAVEL_SUPPORT
 endmenu
 
 source "arch/um/drivers/Kconfig"
+
+config ARCH_SUSPEND_POSSIBLE
+	def_bool y
+
+source "kernel/power/Kconfig"
diff --git a/arch/um/include/shared/kern_util.h b/arch/um/include/shared/kern_util.h
index ccafb62e8cce..9c08e728a675 100644
--- a/arch/um/include/shared/kern_util.h
+++ b/arch/um/include/shared/kern_util.h
@@ -39,6 +39,8 @@ extern int is_syscall(unsigned long addr);
 
 extern void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs);
 
+extern void uml_pm_wake(void);
+
 extern int start_uml(void);
 extern void paging_init(void);
 
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index c89ce642b0d3..5992157ab63f 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -241,6 +241,7 @@ extern int set_signals(int enable);
 extern int set_signals_trace(int enable);
 extern int os_is_signal_stack(void);
 extern void deliver_alarm(void);
+extern void register_pm_wake_signal(void);
 
 /* util.c */
 extern void stack_protections(unsigned long address);
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 00141e70de56..15b6792134b6 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -13,6 +13,7 @@
 #include <linux/sched.h>
 #include <linux/sched/task.h>
 #include <linux/kmsg_dump.h>
+#include <linux/suspend.h>
 
 #include <asm/processor.h>
 #include <asm/sections.h>
@@ -377,3 +378,27 @@ void *text_poke(void *addr, const void *opcode, size_t len)
 void text_poke_sync(void)
 {
 }
+
+#ifdef CONFIG_PM_SLEEP
+void uml_pm_wake(void)
+{
+	pm_system_wakeup();
+}
+
+static int init_pm_wake_signal(void)
+{
+	/*
+	 * In external time-travel mode we can't use signals to wake up
+	 * since that would mess with the scheduling. We'll have to do
+	 * some additional work to support wakeup on virtio devices or
+	 * similar, perhaps implementing a fake RTC controller that can
+	 * trigger wakeup (and request the appropriate scheduling from
+	 * the external scheduler when going to suspend.)
+	 */
+	if (time_travel_mode != TT_MODE_EXTERNAL)
+		register_pm_wake_signal();
+	return 0;
+}
+
+late_initcall(init_pm_wake_signal);
+#endif
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index b58bc68cbe64..0a2ea84033b4 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -136,6 +136,16 @@ void set_sigstack(void *sig_stack, int size)
 		panic("enabling signal stack failed, errno = %d\n", errno);
 }
 
+static void sigusr1_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
+{
+	uml_pm_wake();
+}
+
+void register_pm_wake_signal(void)
+{
+	set_handler(SIGUSR1);
+}
+
 static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
 	[SIGSEGV] = sig_handler,
 	[SIGBUS] = sig_handler,
@@ -145,7 +155,9 @@ static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
 
 	[SIGIO] = sig_handler,
 	[SIGWINCH] = sig_handler,
-	[SIGALRM] = timer_alarm_handler
+	[SIGALRM] = timer_alarm_handler,
+
+	[SIGUSR1] = sigusr1_handler,
 };
 
 static void hard_handler(int sig, siginfo_t *si, void *p)
-- 
2.26.2