[PATCH v2] vfio: platform: Fix using devices in PM Domains

[Geert Uytterhoeven <geert+renesas@glider.be>]

If a device is part of a PM Domain (e.g. power and/or clock domain), its
power state is managed using Runtime PM.  Without Runtime PM, the device
may not be powered up or clocked, causing subtle failures, crashes, or
system lock-ups when the device is accessed by the guest.

Fix this by adding Runtime PM support, powering the device when the VFIO
device is opened by the guest.

Note that while more fine-grained power management could be implemented
on the guest side, if exported by the host, this would be inherently
unsafe, as abusing it may take down the whole system.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
---
v2:
  - Improve wording,
  - Add Reviewed-by.
---
 drivers/vfio/platform/vfio_platform_common.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
index b60bb5326668498c..41f862f055054543 100644
--- a/drivers/vfio/platform/vfio_platform_common.c
+++ b/drivers/vfio/platform/vfio_platform_common.c
@@ -17,6 +17,7 @@
 #include <linux/iommu.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/pm_runtime.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
@@ -233,6 +234,8 @@ static void vfio_platform_release(void *device_data)
 		const char *extra_dbg = NULL;
 		int ret;
 
+		pm_runtime_put(vdev->device);
+
 		ret = vfio_platform_call_reset(vdev, &extra_dbg);
 		if (ret && vdev->reset_required) {
 			dev_warn(vdev->device, "reset driver is required and reset call failed in release (%d) %s\n",
@@ -275,6 +278,10 @@ static int vfio_platform_open(void *device_data)
 				 ret, extra_dbg ? extra_dbg : "");
 			goto err_rst;
 		}
+
+		ret = pm_runtime_get_sync(vdev->device);
+		if (ret < 0)
+			goto err_rst;
 	}
 
 	vdev->refcnt++;
@@ -690,6 +697,7 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
 
 	mutex_init(&vdev->igate);
 
+	pm_runtime_enable(vdev->device);
 	return 0;
 
 put_iommu:
@@ -707,6 +715,7 @@ struct vfio_platform_device *vfio_platform_remove_common(struct device *dev)
 	vdev = vfio_del_group_dev(dev);
 
 	if (vdev) {
+		pm_runtime_disable(vdev->device);
 		vfio_platform_put_reset(vdev);
 		vfio_iommu_group_put(dev->iommu_group, dev);
 	}
-- 
2.7.4