Subject: Re: [PATCH 04/26] vfio: Add struct to hold KVM assets and dedup group vs. iommufd code

From: Alex Williamson <[email-masked]>
Date: Thu, 28 Sep 2023 16:21:08 -0600

On Fri, 15 Sep 2023 17:30:56 -0700
Sean Christopherson <[email-masked]> wrote:

> Add a struct to hold the KVM assets need to manage and pass along KVM
> references to VFIO devices.  Providing a common struct deduplicates the
> group vs. iommufd code, and will make it easier to rework the attachment
> logic so that VFIO doesn't have to do a symbol lookup to retrieve the
> get/put helpers from KVM.
> 
> Signed-off-by: Sean Christopherson <[email-masked]>
> ---
>  drivers/vfio/device_cdev.c |  9 +-------
>  drivers/vfio/group.c       | 18 ++--------------
>  drivers/vfio/vfio.h        | 22 +++++++++----------
>  drivers/vfio/vfio_main.c   | 43 +++++++++++++++++++++++++++-----------
>  4 files changed, 45 insertions(+), 47 deletions(-)

Reviewed-by: Alex Williamson <[email-masked]>

> diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> index e75da0a70d1f..e484d6d6400a 100644
> --- a/drivers/vfio/device_cdev.c
> +++ b/drivers/vfio/device_cdev.c
> @@ -46,13 +46,6 @@ int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
>  	return ret;
>  }
>  
> -static void vfio_df_get_kvm_safe(struct vfio_device_file *df)
> -{
> -	spin_lock(&df->kvm_ref_lock);
> -	vfio_device_get_kvm_safe(df->device, df->kvm);
> -	spin_unlock(&df->kvm_ref_lock);
> -}
> -
>  long vfio_df_ioctl_bind_iommufd(struct vfio_device_file *df,
>  				struct vfio_device_bind_iommufd __user *arg)
>  {
> @@ -99,7 +92,7 @@ long vfio_df_ioctl_bind_iommufd(struct vfio_device_file *df,
>  	 * a reference.  This reference is held until device closed.
>  	 * Save the pointer in the device for use by drivers.
>  	 */
> -	vfio_df_get_kvm_safe(df);
> +	vfio_device_get_kvm_safe(df->device, &df->kvm_ref);
>  
>  	ret = vfio_df_open(df);
>  	if (ret)
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index 610a429c6191..756e47ff4cf0 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -157,13 +157,6 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group,
>  	return ret;
>  }
>  
> -static void vfio_device_group_get_kvm_safe(struct vfio_device *device)
> -{
> -	spin_lock(&device->group->kvm_ref_lock);
> -	vfio_device_get_kvm_safe(device, device->group->kvm);
> -	spin_unlock(&device->group->kvm_ref_lock);
> -}
> -
>  static int vfio_df_group_open(struct vfio_device_file *df)
>  {
>  	struct vfio_device *device = df->device;
> @@ -184,7 +177,7 @@ static int vfio_df_group_open(struct vfio_device_file *df)
>  	 * the pointer in the device for use by drivers.
>  	 */
>  	if (device->open_count == 0)
> -		vfio_device_group_get_kvm_safe(device);
> +		vfio_device_get_kvm_safe(device, &device->group->kvm_ref);
>  
>  	df->iommufd = device->group->iommufd;
>  	if (df->iommufd && vfio_device_is_noiommu(device) && device->open_count == 0) {
> @@ -560,7 +553,7 @@ static struct vfio_group *vfio_group_alloc(struct iommu_group *iommu_group,
>  
>  	refcount_set(&group->drivers, 1);
>  	mutex_init(&group->group_lock);
> -	spin_lock_init(&group->kvm_ref_lock);
> +	spin_lock_init(&group->kvm_ref.lock);
>  	INIT_LIST_HEAD(&group->device_list);
>  	mutex_init(&group->device_lock);
>  	group->iommu_group = iommu_group;
> @@ -884,13 +877,6 @@ bool vfio_group_enforced_coherent(struct vfio_group *group)
>  	return ret;
>  }
>  
> -void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
> -{
> -	spin_lock(&group->kvm_ref_lock);
> -	group->kvm = kvm;
> -	spin_unlock(&group->kvm_ref_lock);
> -}
> -
>  /**
>   * vfio_file_has_dev - True if the VFIO file is a handle for device
>   * @file: VFIO file to check
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index c26d1ad68105..a1f741365075 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -12,18 +12,23 @@
>  #include <linux/module.h>
>  #include <linux/vfio.h>
>  
> +struct kvm;
>  struct iommufd_ctx;
>  struct iommu_group;
>  struct vfio_container;
>  
> +struct vfio_kvm_reference {
> +	struct kvm			*kvm;
> +	spinlock_t			lock;
> +};
> +
>  struct vfio_device_file {
>  	struct vfio_device *device;
>  	struct vfio_group *group;
>  
>  	u8 access_granted;
>  	u32 devid; /* only valid when iommufd is valid */
> -	spinlock_t kvm_ref_lock; /* protect kvm field */
> -	struct kvm *kvm;
> +	struct vfio_kvm_reference kvm_ref;
>  	struct iommufd_ctx *iommufd; /* protected by struct vfio_device_set::lock */
>  };
>  
> @@ -88,11 +93,10 @@ struct vfio_group {
>  #endif
>  	enum vfio_group_type		type;
>  	struct mutex			group_lock;
> -	struct kvm			*kvm;
> +	struct vfio_kvm_reference	kvm_ref;
>  	struct file			*opened_file;
>  	struct blocking_notifier_head	notifier;
>  	struct iommufd_ctx		*iommufd;
> -	spinlock_t			kvm_ref_lock;
>  	unsigned int			cdev_device_open_cnt;
>  };
>  
> @@ -108,7 +112,6 @@ void vfio_device_group_unuse_iommu(struct vfio_device *device);
>  void vfio_df_group_close(struct vfio_device_file *df);
>  struct vfio_group *vfio_group_from_file(struct file *file);
>  bool vfio_group_enforced_coherent(struct vfio_group *group);
> -void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm);
>  bool vfio_device_has_container(struct vfio_device *device);
>  int __init vfio_group_init(void);
>  void vfio_group_cleanup(void);
> @@ -171,10 +174,6 @@ static inline bool vfio_group_enforced_coherent(struct vfio_group *group)
>  	return true;
>  }
>  
> -static inline void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
> -{
> -}
> -
>  static inline bool vfio_device_has_container(struct vfio_device *device)
>  {
>  	return false;
> @@ -435,11 +434,12 @@ static inline void vfio_virqfd_exit(void)
>  #endif
>  
>  #if IS_ENABLED(CONFIG_KVM)
> -void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm);
> +void vfio_device_get_kvm_safe(struct vfio_device *device,
> +			      struct vfio_kvm_reference *ref);
>  void vfio_device_put_kvm(struct vfio_device *device);
>  #else
>  static inline void vfio_device_get_kvm_safe(struct vfio_device *device,
> -					    struct kvm *kvm)
> +					    struct vfio_kvm_reference *ref)
>  {
>  }
>  
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 124cc88966a7..e77e8c6aae2f 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -397,7 +397,7 @@ vfio_allocate_device_file(struct vfio_device *device)
>  		return ERR_PTR(-ENOMEM);
>  
>  	df->device = device;
> -	spin_lock_init(&df->kvm_ref_lock);
> +	spin_lock_init(&df->kvm_ref.lock);
>  
>  	return df;
>  }
> @@ -1303,7 +1303,8 @@ bool vfio_file_enforced_coherent(struct file *file)
>  EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
>  
>  #if IS_ENABLED(CONFIG_KVM)
> -void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
> +void vfio_device_get_kvm_safe(struct vfio_device *device,
> +			      struct vfio_kvm_reference *ref)
>  {
>  	void (*pfn)(struct kvm *kvm);
>  	bool (*fn)(struct kvm *kvm);
> @@ -1311,28 +1312,33 @@ void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
>  
>  	lockdep_assert_held(&device->dev_set->lock);
>  
> -	if (!kvm)
> -		return;
> +	spin_lock(&ref->lock);
> +
> +	if (!ref->kvm)
> +		goto out;
>  
>  	pfn = symbol_get(kvm_put_kvm);
>  	if (WARN_ON(!pfn))
> -		return;
> +		goto out;
>  
>  	fn = symbol_get(kvm_get_kvm_safe);
>  	if (WARN_ON(!fn)) {
>  		symbol_put(kvm_put_kvm);
> -		return;
> +		goto out;
>  	}
>  
> -	ret = fn(kvm);
> +	ret = fn(ref->kvm);
>  	symbol_put(kvm_get_kvm_safe);
>  	if (!ret) {
>  		symbol_put(kvm_put_kvm);
> -		return;
> +		goto out;
>  	}
>  
>  	device->put_kvm = pfn;
> -	device->kvm = kvm;
> +	device->kvm = ref->kvm;
> +
> +out:
> +	spin_unlock(&ref->lock);
>  }
>  
>  void vfio_device_put_kvm(struct vfio_device *device)
> @@ -1353,6 +1359,21 @@ void vfio_device_put_kvm(struct vfio_device *device)
>  	device->kvm = NULL;
>  }
>  
> +static void vfio_device_set_kvm(struct vfio_kvm_reference *ref,
> +				struct kvm *kvm)
> +{
> +	spin_lock(&ref->lock);
> +	ref->kvm = kvm;
> +	spin_unlock(&ref->lock);
> +}
> +
> +static void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
> +{
> +#if IS_ENABLED(CONFIG_VFIO_GROUP)
> +	vfio_device_set_kvm(&group->kvm_ref, kvm);
> +#endif
> +}
> +
>  static void vfio_device_file_set_kvm(struct file *file, struct kvm *kvm)
>  {
>  	struct vfio_device_file *df = file->private_data;
> @@ -1362,9 +1383,7 @@ static void vfio_device_file_set_kvm(struct file *file, struct kvm *kvm)
>  	 * be propagated to vfio_device::kvm when the file is bound to
>  	 * iommufd successfully in the vfio device cdev path.
>  	 */
> -	spin_lock(&df->kvm_ref_lock);
> -	df->kvm = kvm;
> -	spin_unlock(&df->kvm_ref_lock);
> +	vfio_device_set_kvm(&df->kvm_ref, kvm);
>  }
>  
>  /**