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

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Date:   Fri, 13 Apr 2018 11:14:29 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Baptiste Reynal <b.reynal@...tualopensystems.com>,
        Alex Williamson <alex.williamson@...hat.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>, kvm@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio: platform: Fix using devices in PM Domains

Hi Geert,

On 11/04/18 11:24, Geert Uytterhoeven wrote:
> 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.
the device may not be powered up/clcoked or power/clock may be switched
off while the guest uses it.
> 
> 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.
Please can you elaborate on this remark please?

Thanks

Eric
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> This depends on "[PATCH v3 2/2] vfio: platform: Add generic DT reset
> support" due to a small contextual change (addition of "#include
> <linux/reset.h>").
> 
>  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 ef9b9e3220ebe939..4db0a143992c3353 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>
> @@ -249,6 +250,8 @@ 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",
> @@ -291,6 +294,10 @@ 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++;
> @@ -706,6 +713,7 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
>  
>  	mutex_init(&vdev->igate);
>  
> +	pm_runtime_enable(vdev->device);
>  	return 0;
>  
>  put_iommu:
> @@ -723,6 +731,7 @@ 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);
>  	}
>