Re: [PATCH v9 06/25] kvm/vfio: Accept vfio device file from userspace

[Eric Auger <eric.auger@redhat.com>]

Hi Yi,

On 4/1/23 17:18, Yi Liu wrote:
> This defines KVM_DEV_VFIO_FILE* and make alias with KVM_DEV_VFIO_GROUP*.
> Old userspace uses KVM_DEV_VFIO_GROUP* works as well.
>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Tested-by: Terrence Xu <terrence.xu@intel.com>
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Tested-by: Yanting Jiang <yanting.jiang@intel.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>  Documentation/virt/kvm/devices/vfio.rst | 53 +++++++++++++++++--------
>  include/uapi/linux/kvm.h                | 16 ++++++--
>  virt/kvm/vfio.c                         | 16 ++++----
>  3 files changed, 56 insertions(+), 29 deletions(-)
>
> diff --git a/Documentation/virt/kvm/devices/vfio.rst b/Documentation/virt/kvm/devices/vfio.rst
> index 79b6811bb4f3..277d727ec1a2 100644
> --- a/Documentation/virt/kvm/devices/vfio.rst
> +++ b/Documentation/virt/kvm/devices/vfio.rst
> @@ -9,24 +9,38 @@ Device types supported:
>    - KVM_DEV_TYPE_VFIO
>  
>  Only one VFIO instance may be created per VM.  The created device
> -tracks VFIO groups in use by the VM and features of those groups
> -important to the correctness and acceleration of the VM.  As groups
> -are enabled and disabled for use by the VM, KVM should be updated
> -about their presence.  When registered with KVM, a reference to the
> -VFIO-group is held by KVM.
> +tracks VFIO files (group or device) in use by the VM and features
> +of those groups/devices important to the correctness and acceleration
> +of the VM.  As groups/devices are enabled and disabled for use by the
> +VM, KVM should be updated about their presence.  When registered with
> +KVM, a reference to the VFIO file is held by KVM.
>  
>  Groups:
> -  KVM_DEV_VFIO_GROUP
> -
> -KVM_DEV_VFIO_GROUP attributes:
> -  KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
> -	kvm_device_attr.addr points to an int32_t file descriptor
> -	for the VFIO group.
> -  KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking
> -	kvm_device_attr.addr points to an int32_t file descriptor
> -	for the VFIO group.
> -  KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE: attaches a guest visible TCE table
> +  KVM_DEV_VFIO_FILE
> +	alias: KVM_DEV_VFIO_GROUP
> +
> +KVM_DEV_VFIO_FILE attributes:
> +  KVM_DEV_VFIO_FILE_ADD: Add a VFIO file (group/device) to VFIO-KVM device
> +	tracking
> +
> +	alias: KVM_DEV_VFIO_GROUP_ADD
> +
> +	kvm_device_attr.addr points to an int32_t file descriptor for the
> +	VFIO file.
> +
> +  KVM_DEV_VFIO_FILE_DEL: Remove a VFIO file (group/device) from VFIO-KVM
> +	device tracking
> +
> +	alias: KVM_DEV_VFIO_GROUP_DEL
> +
> +	kvm_device_attr.addr points to an int32_t file descriptor for the
> +	VFIO file.
> +
> +  KVM_DEV_VFIO_FILE_SET_SPAPR_TCE: attaches a guest visible TCE table
>  	allocated by sPAPR KVM.
> +
> +	alias: KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE
> +
>  	kvm_device_attr.addr points to a struct::
>  
>  		struct kvm_vfio_spapr_tce {
> @@ -40,9 +54,14 @@ KVM_DEV_VFIO_GROUP attributes:
>  	- @tablefd is a file descriptor for a TCE table allocated via
>  	  KVM_CREATE_SPAPR_TCE.
>  
> +	only accepts vfio group file as SPAPR has no iommufd support
So then what is the point of introducing

KVM_DEV_VFIO_FILE_SET_SPAPR_TCE at this stage?

I think would have separated the

Groups:
  KVM_DEV_VFIO_FILE
	alias: KVM_DEV_VFIO_GROUP

KVM_DEV_VFIO_FILE attributes:
  KVM_DEV_VFIO_FILE_ADD: Add a VFIO file (group/device) to VFIO-KVM device
	tracking

	kvm_device_attr.addr points to an int32_t file descriptor for the
	VFIO file.

  KVM_DEV_VFIO_FILE_DEL: Remove a VFIO file (group/device) from VFIO-KVM
	device tracking

	kvm_device_attr.addr points to an int32_t file descriptor for the
	VFIO file.

KVM_DEV_VFIO_GROUP (legacy kvm device group restricted to the handling of VFIO group fd)
  KVM_DEV_VFIO_GROUP_ADD: same as KVM_DEV_VFIO_FILE_ADD for group fd only
  KVM_DEV_VFIO_GROUP_DEL: same as KVM_DEV_VFIO_FILE_DEL for group fd only
  KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE: attaches a guest visible TCE table
	allocated by sPAPR KVM.
	kvm_device_attr.addr points to a struct::

		struct kvm_vfio_spapr_tce {
			__s32	groupfd;
			__s32	tablefd;
		};

	where:

	- @groupfd is a file descriptor for a VFIO group;
	- @tablefd is a file descriptor for a TCE table allocated via
	  KVM_CREATE_SPAPR_TCE.


You don't say anything about potential restriction, ie. what if the user calls KVM_DEV_VFIO_FILE with device fds while it has been using legacy container/group API?

Thanks

Eric

> +
>  ::
>  
> -The GROUP_ADD operation above should be invoked prior to accessing the
> +The FILE/GROUP_ADD operation above should be invoked prior to accessing the
>  device file descriptor via VFIO_GROUP_GET_DEVICE_FD in order to support
>  drivers which require a kvm pointer to be set in their .open_device()
> -callback.
> +callback.  It is the same for device file descriptor via character device
> +open which gets device access via VFIO_DEVICE_BIND_IOMMUFD.  For such file
> +descriptors, FILE_ADD should be invoked before VFIO_DEVICE_BIND_IOMMUFD
> +to support the drivers mentioned in prior sentence as well.
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index d77aef872a0a..a8eeca70a498 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1410,10 +1410,18 @@ struct kvm_device_attr {
>  	__u64	addr;		/* userspace address of attr data */
>  };
>  
> -#define  KVM_DEV_VFIO_GROUP			1
> -#define   KVM_DEV_VFIO_GROUP_ADD			1
> -#define   KVM_DEV_VFIO_GROUP_DEL			2
> -#define   KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE		3
> +#define  KVM_DEV_VFIO_FILE	1
> +
> +#define   KVM_DEV_VFIO_FILE_ADD			1
> +#define   KVM_DEV_VFIO_FILE_DEL			2
> +#define   KVM_DEV_VFIO_FILE_SET_SPAPR_TCE	3
> +
> +/* KVM_DEV_VFIO_GROUP aliases are for compile time uapi compatibility */
> +#define  KVM_DEV_VFIO_GROUP	KVM_DEV_VFIO_FILE
> +
> +#define   KVM_DEV_VFIO_GROUP_ADD	KVM_DEV_VFIO_FILE_ADD
> +#define   KVM_DEV_VFIO_GROUP_DEL	KVM_DEV_VFIO_FILE_DEL
> +#define   KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE	KVM_DEV_VFIO_FILE_SET_SPAPR_TCE
>  
>  enum kvm_device_type {
>  	KVM_DEV_TYPE_FSL_MPIC_20	= 1,
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index 857d6ba349e1..d869913baafd 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -286,18 +286,18 @@ static int kvm_vfio_set_file(struct kvm_device *dev, long attr,
>  	int32_t fd;
>  
>  	switch (attr) {
> -	case KVM_DEV_VFIO_GROUP_ADD:
> +	case KVM_DEV_VFIO_FILE_ADD:
>  		if (get_user(fd, argp))
>  			return -EFAULT;
>  		return kvm_vfio_file_add(dev, fd);
>  
> -	case KVM_DEV_VFIO_GROUP_DEL:
> +	case KVM_DEV_VFIO_FILE_DEL:
>  		if (get_user(fd, argp))
>  			return -EFAULT;
>  		return kvm_vfio_file_del(dev, fd);
>  
>  #ifdef CONFIG_SPAPR_TCE_IOMMU
> -	case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE:
> +	case KVM_DEV_VFIO_FILE_SET_SPAPR_TCE:
>  		return kvm_vfio_file_set_spapr_tce(dev, arg);
>  #endif
>  	}
> @@ -309,7 +309,7 @@ static int kvm_vfio_set_attr(struct kvm_device *dev,
>  			     struct kvm_device_attr *attr)
>  {
>  	switch (attr->group) {
> -	case KVM_DEV_VFIO_GROUP:
> +	case KVM_DEV_VFIO_FILE:
>  		return kvm_vfio_set_file(dev, attr->attr,
>  					 u64_to_user_ptr(attr->addr));
>  	}
> @@ -321,12 +321,12 @@ static int kvm_vfio_has_attr(struct kvm_device *dev,
>  			     struct kvm_device_attr *attr)
>  {
>  	switch (attr->group) {
> -	case KVM_DEV_VFIO_GROUP:
> +	case KVM_DEV_VFIO_FILE:
>  		switch (attr->attr) {
> -		case KVM_DEV_VFIO_GROUP_ADD:
> -		case KVM_DEV_VFIO_GROUP_DEL:
> +		case KVM_DEV_VFIO_FILE_ADD:
> +		case KVM_DEV_VFIO_FILE_DEL:
>  #ifdef CONFIG_SPAPR_TCE_IOMMU
> -		case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE:
> +		case KVM_DEV_VFIO_FILE_SET_SPAPR_TCE:
>  #endif
>  			return 0;
>  		}