linux-kernel - Re: [PATCH v3 6/8] vfio: Invoke runtime PM API for IOCTL request

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Date:   Thu, 5 May 2022 15:10:43 +0530
From:   Abhishek Sahu <abhsahu@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Cornelia Huck <cohuck@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
        Kevin Tian <kevin.tian@...el.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v3 6/8] vfio: Invoke runtime PM API for IOCTL request

On 5/5/2022 1:12 AM, Alex Williamson wrote:
> On Mon, 25 Apr 2022 14:56:13 +0530
> Abhishek Sahu <abhsahu@...dia.com> wrote:
> 
>> The vfio/pci driver will have runtime power management support where the
>> user can put the device low power state and then PCI devices can go into
>> the D3cold state. If the device is in low power state and user issues any
>> IOCTL, then the device should be moved out of low power state first. Once
>> the IOCTL is serviced, then it can go into low power state again. The
>> runtime PM framework manages this with help of usage count. One option
>> was to add the runtime PM related API's inside vfio/pci driver but some
>> IOCTL (like VFIO_DEVICE_FEATURE) can follow a different path and more
>> IOCTL can be added in the future. Also, the runtime PM will be
>> added for vfio/pci based drivers variant currently but the other vfio
>> based drivers can use the same in the future. So, this patch adds the
>> runtime calls runtime related API in the top level IOCTL function itself.
>>
>> For the vfio drivers which do not have runtime power management support
>> currently, the runtime PM API's won't be invoked. Only for vfio/pci
>> based drivers currently, the runtime PM API's will be invoked to increment
>> and decrement the usage count. Taking this usage count incremented while
>> servicing IOCTL will make sure that user won't put the device into low
>> power state when any other IOCTL is being serviced in parallel.
>>
>> Signed-off-by: Abhishek Sahu <abhsahu@...dia.com>
>> ---
>>  drivers/vfio/vfio.c | 44 +++++++++++++++++++++++++++++++++++++++++---
>>  1 file changed, 41 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
>> index a4555014bd1e..4e65a127744e 100644
>> --- a/drivers/vfio/vfio.c
>> +++ b/drivers/vfio/vfio.c
>> @@ -32,6 +32,7 @@
>>  #include <linux/vfio.h>
>>  #include <linux/wait.h>
>>  #include <linux/sched/signal.h>
>> +#include <linux/pm_runtime.h>
>>  #include "vfio.h"
>>  
>>  #define DRIVER_VERSION	"0.3"
>> @@ -1536,6 +1537,30 @@ static const struct file_operations vfio_group_fops = {
>>  	.release	= vfio_group_fops_release,
>>  };
>>  
>> +/*
>> + * Wrapper around pm_runtime_resume_and_get().
>> + * Return 0, if driver power management callbacks are not present i.e. the driver is not
> 
> Mind the gratuitous long comment line here.
> 
 
 Thanks Alex.
 
 That was a miss. I will fix this.
 
>> + * using runtime power management.
>> + * Return 1 upon success, otherwise -errno
> 
> Changing semantics vs the thing we're wrapping, why not provide a
> wrapper for the `put` as well to avoid?  The only cases where we return
> zero are just as easy to detect on the other side.
> 

 Yes. Using wrapper function for put is better option.
 I will make the changes.

>> + */
>> +static inline int vfio_device_pm_runtime_get(struct device *dev)
> 
> Given some of Jason's recent series, this should probably just accept a
> vfio_device.
> 

 Sorry. I didn't get this part.

 Do I need to change it to

 static inline int vfio_device_pm_runtime_get(struct vfio_device *device)
 {
    struct device *dev = device->dev;
    ...
 }

>> +{
>> +#ifdef CONFIG_PM
>> +	int ret;
>> +
>> +	if (!dev->driver || !dev->driver->pm)
>> +		return 0;
>> +
>> +	ret = pm_runtime_resume_and_get(dev);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	return 1;
>> +#else
>> +	return 0;
>> +#endif
>> +}
>> +
>>  /*
>>   * VFIO Device fd
>>   */
>> @@ -1845,15 +1870,28 @@ static long vfio_device_fops_unl_ioctl(struct file *filep,
>>  				       unsigned int cmd, unsigned long arg)
>>  {
>>  	struct vfio_device *device = filep->private_data;
>> +	int pm_ret, ret = 0;
>> +
>> +	pm_ret = vfio_device_pm_runtime_get(device->dev);
>> +	if (pm_ret < 0)
>> +		return pm_ret;
> 
> I wonder if we might simply want to mask pm errors behind -EIO, maybe
> with a rate limited dev_info().  My concern would be that we might mask
> errnos that userspace has come to expect for certain ioctls.  Thanks,
> 
> Alex
> 

  I need to do something like following. Correct ?

  ret = vfio_device_pm_runtime_get(device);
  if (ret < 0) {
     dev_info_ratelimited(device->dev, "vfio: runtime resume failed %d\n", ret);
     return -EIO;
  }
  
  Regards,
  Abhishek
 
>>  
>>  	switch (cmd) {
>>  	case VFIO_DEVICE_FEATURE:
>> -		return vfio_ioctl_device_feature(device, (void __user *)arg);
>> +		ret = vfio_ioctl_device_feature(device, (void __user *)arg);
>> +		break;
>>  	default:
>>  		if (unlikely(!device->ops->ioctl))
>> -			return -EINVAL;
>> -		return device->ops->ioctl(device, cmd, arg);
>> +			ret = -EINVAL;
>> +		else
>> +			ret = device->ops->ioctl(device, cmd, arg);
>> +		break;
>>  	}
>> +
>> +	if (pm_ret)
>> +		pm_runtime_put(device->dev);
>> +
>> +	return ret;
>>  }
>>  
>>  static ssize_t vfio_device_fops_read(struct file *filep, char __user *buf,
>