linux-kernel - [PATCH] vfio: platform: Fix using devices in PM Domains

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Date:   Wed, 11 Apr 2018 11:15:46 +0200
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Baptiste Reynal <b.reynal@...tualopensystems.com>,
        Alex Williamson <alex.williamson@...hat.com>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, kvm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH] vfio: platform: Fix using devices in PM Domains

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, 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, this would be inherently unsafe, as
abusing it may kill the whole system.

Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
 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 3c13327b2777f8ec..9d46fce2446daebe 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/reset.h>
 #include <linux/slab.h>
 #include <linux/types.h>
@@ -255,6 +256,8 @@ 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",
@@ -297,6 +300,10 @@ 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++;
@@ -712,6 +719,7 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
 
 	mutex_init(&vdev->igate);
 
+	pm_runtime_enable(vdev->device);
 	return 0;
 
 put_iommu:
@@ -729,6 +737,7 @@ 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