linux-kernel - [PATCH RFC v2] misc/pvpanic: add support for normal shutdowns

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Message-Id: <20240412-pvpanic-shutdown-v2-1-5e544417bc17@weissschuh.net>
Date: Fri, 12 Apr 2024 00:03:57 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Arnd Bergmann <arnd@...db.de>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH RFC v2] misc/pvpanic: add support for normal shutdowns

Shutdown requests are normally hardware dependent.
By extending pvpanic to also handle shutdown requests, guests can
submit such requests with an easily implementable and cross-platform
mechanism.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
To: Arnd Bergmann <arnd@...db.de>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>

Changes in v2:
- Drop RFC status
- Drop define from header file as it was submitted on its own
- Handle disabling of handler through sysfs
- Link to v1: https://lore.kernel.org/r/20231104-pvpanic-shutdown-v1-1-5ee7c9b3e301@weissschuh.net
---
This patch is based on char-misc/char-misc-testing as it depends on
commit ad76f3e8f57c ("misc/pvpanic: add shutdown event definition")

The corresponding patch to qemu has also been submitted[0].
General discussions about the feature should happen on the other thread.

[0] https://lore.kernel.org/qemu-devel/20231104-pvpanic-shutdown-v1-0-02353157891b@t-8ch.de/
---
 drivers/misc/pvpanic/pvpanic.c | 43 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/pvpanic/pvpanic.c b/drivers/misc/pvpanic/pvpanic.c
index df3457ce1cb1..17c0eb549463 100644
--- a/drivers/misc/pvpanic/pvpanic.c
+++ b/drivers/misc/pvpanic/pvpanic.c
@@ -19,6 +19,7 @@
 #include <linux/module.h>
 #include <linux/panic_notifier.h>
 #include <linux/platform_device.h>
+#include <linux/reboot.h>
 #include <linux/spinlock.h>
 #include <linux/sysfs.h>
 #include <linux/types.h>
@@ -35,6 +36,7 @@ struct pvpanic_instance {
 	void __iomem *base;
 	unsigned int capability;
 	unsigned int events;
+	struct sys_off_handler *sys_off;
 	struct list_head list;
 };
 
@@ -78,6 +80,39 @@ static struct notifier_block pvpanic_panic_nb = {
 	.priority = INT_MAX,
 };
 
+static int pvpanic_sys_off(struct sys_off_data *data)
+{
+	pvpanic_send_event(PVPANIC_SHUTDOWN);
+
+	return NOTIFY_DONE;
+}
+
+static void pvpanic_synchronize_sys_off_handler(struct device *dev, struct pvpanic_instance *pi)
+{
+	/* The kernel core has logic to fall back to system halt if no
+	 * sys_off_handler is registered.
+	 * When the pvpanic sys_off_handler is disabled via sysfs the kernel
+	 * should use that fallback logic, so the handler needs to be unregistered.
+	 */
+
+	struct sys_off_handler *sys_off;
+
+	if (!(pi->events & PVPANIC_SHUTDOWN) == !pi->sys_off)
+		return;
+
+	if (!pi->sys_off) {
+		sys_off = register_sys_off_handler(SYS_OFF_MODE_POWER_OFF, SYS_OFF_PRIO_LOW,
+						   pvpanic_sys_off, NULL);
+		if (IS_ERR(sys_off))
+			dev_warn(dev, "Could not register sys_off_handler: %pe\n", sys_off);
+		else
+			pi->sys_off = sys_off;
+	} else {
+		unregister_sys_off_handler(pi->sys_off);
+		pi->sys_off = NULL;
+	}
+}
+
 static void pvpanic_remove(void *param)
 {
 	struct pvpanic_instance *pi_cur, *pi_next;
@@ -91,6 +126,8 @@ static void pvpanic_remove(void *param)
 		}
 	}
 	spin_unlock(&pvpanic_lock);
+
+	unregister_sys_off_handler(pi->sys_off);
 }
 
 static ssize_t capability_show(struct device *dev, struct device_attribute *attr, char *buf)
@@ -123,6 +160,7 @@ static ssize_t events_store(struct device *dev, struct device_attribute *attr,
 		return -EINVAL;
 
 	pi->events = tmp;
+	pvpanic_synchronize_sys_off_handler(dev, pi);
 
 	return count;
 }
@@ -156,12 +194,15 @@ int devm_pvpanic_probe(struct device *dev, void __iomem *base)
 		return -ENOMEM;
 
 	pi->base = base;
-	pi->capability = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
+	pi->capability = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED | PVPANIC_SHUTDOWN;
 
 	/* initlize capability by RDPT */
 	pi->capability &= ioread8(base);
 	pi->events = pi->capability;
 
+	pi->sys_off = NULL;
+	pvpanic_synchronize_sys_off_handler(dev, pi);
+
 	spin_lock(&pvpanic_lock);
 	list_add(&pi->list, &pvpanic_list);
 	spin_unlock(&pvpanic_lock);

---
base-commit: dc806bd48abc1b8a4ae72709a37e65db42a32048
change-id: 20231104-pvpanic-shutdown-5fa38a879ad1

Best regards,
-- 
Thomas Weißschuh <linux@...ssschuh.net>