Re: [PATCH 03/13] vfio: Accept vfio device file in the driver facing kAPI

From: Eric Auger <eric.auger@redhat.com>
To: Yi Liu <yi.l.liu@intel.com>, alex.williamson@redhat.com, jgg@nvidia.com
Cc: kevin.tian@intel.com, cohuck@redhat.com, nicolinc@nvidia.com,
	kvm@vger.kernel.org, mjrosato@linux.ibm.com,
	chao.p.peng@linux.intel.com, yi.y.sun@linux.intel.com,
	peterx@redhat.com, jasowang@redhat.com,
	suravee.suthikulpanit@amd.com
Subject: Re: [PATCH 03/13] vfio: Accept vfio device file in the driver facing kAPI
Date: Wed, 18 Jan 2023 17:11:07 +0100	[thread overview]
Message-ID: <6c95aefd-31f5-fc98-7a51-77f181dc6ec8@redhat.com> (raw)
In-Reply-To: <20230117134942.101112-4-yi.l.liu@intel.com>

Hi Yi,

On 1/17/23 14:49, Yi Liu wrote:
> This makes the vfio file kAPIs to accepte vfio device files, also a
> preparation for vfio device cdev support.
>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>  drivers/vfio/vfio.h      |  1 +
>  drivers/vfio/vfio_main.c | 51 ++++++++++++++++++++++++++++++++++++----
>  2 files changed, 48 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index ef5de2872983..53af6e3ea214 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -18,6 +18,7 @@ struct vfio_container;
>  
>  struct vfio_device_file {
>  	struct vfio_device *device;
> +	struct kvm *kvm;
>  };
>  
>  void vfio_device_put_registration(struct vfio_device *device);
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 1aedfbd15ca0..dc08d5dd62cc 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -1119,13 +1119,23 @@ const struct file_operations vfio_device_fops = {
>  	.mmap		= vfio_device_fops_mmap,
>  };
>  
> +static struct vfio_device *vfio_device_from_file(struct file *file)
> +{
> +	struct vfio_device_file *df = file->private_data;
> +
> +	if (file->f_op != &vfio_device_fops)
> +		return NULL;
> +	return df->device;
> +}
> +
>  /**
>   * vfio_file_is_valid - True if the file is usable with VFIO aPIS
>   * @file: VFIO group file or VFIO device file
>   */
>  bool vfio_file_is_valid(struct file *file)
>  {
> -	return vfio_group_from_file(file);
> +	return vfio_group_from_file(file) ||
> +	       vfio_device_from_file(file);
>  }
>  EXPORT_SYMBOL_GPL(vfio_file_is_valid);
>  
> @@ -1140,15 +1150,37 @@ EXPORT_SYMBOL_GPL(vfio_file_is_valid);
>   */
>  bool vfio_file_enforced_coherent(struct file *file)
>  {
> -	struct vfio_group *group = vfio_group_from_file(file);
> +	struct vfio_group *group;
> +	struct vfio_device *device;
>  
> +	group = vfio_group_from_file(file);
>  	if (group)
>  		return vfio_group_enforced_coherent(group);
>  
> +	device = vfio_device_from_file(file);
> +	if (device)
> +		return device_iommu_capable(device->dev,
> +					    IOMMU_CAP_ENFORCE_CACHE_COHERENCY);
> +
>  	return true;
>  }
>  EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
>  
> +static void vfio_device_file_set_kvm(struct file *file, struct kvm *kvm)
> +{
> +	struct vfio_device_file *df = file->private_data;
> +	struct vfio_device *device = df->device;
> +
> +	/*
> +	 * The kvm is first recorded in the df, and will be propagated
> +	 * to vfio_device::kvm when the file binds iommufd successfully in
> +	 * the vfio device cdev path.
> +	 */
> +	mutex_lock(&device->dev_set->lock);
it is not totally obvious to me why the

device->dev_set->lock needs to be held here and why that lock in particular. Isn't supposed to protect the vfio_device_set. The header just mentions
"the VFIO core will provide a lock that is held around open_device()/close_device() for all devices in the set."

> +	df->kvm = kvm;
> +	mutex_unlock(&device->dev_set->lock);
> +}
> +
>  /**
>   * vfio_file_set_kvm - Link a kvm with VFIO drivers
>   * @file: VFIO group file or device file
> @@ -1157,10 +1189,14 @@ EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
>   */
>  void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
>  {
> -	struct vfio_group *group = vfio_group_from_file(file);
> +	struct vfio_group *group;
>  
> +	group = vfio_group_from_file(file);
>  	if (group)
>  		vfio_group_set_kvm(group, kvm);
> +
> +	if (vfio_device_from_file(file))
> +		vfio_device_file_set_kvm(file, kvm);
>  }
>  EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
>  
> @@ -1173,10 +1209,17 @@ EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
>   */
>  bool vfio_file_has_dev(struct file *file, struct vfio_device *device)
>  {
> -	struct vfio_group *group = vfio_group_from_file(file);
> +	struct vfio_group *group;
> +	struct vfio_device *vdev;
>  
> +	group = vfio_group_from_file(file);
>  	if (group)
>  		return vfio_group_has_dev(group, device);
> +
> +	vdev = vfio_device_from_file(file);
> +	if (device)
> +		return vdev == device;
> +
>  	return false;
>  }
>  EXPORT_SYMBOL_GPL(vfio_file_has_dev);
Thanks

Eric