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

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Hi Eric,

> From: Eric Auger <eric.auger@xxxxxxxxxx>
> Sent: Thursday, April 6, 2023 5:47 PM
> 
> 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@xxxxxxxxxx>
> > Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> > Tested-by: Terrence Xu <terrence.xu@xxxxxxxxx>
> > Tested-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> > Tested-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> > Tested-by: Yanting Jiang <yanting.jiang@xxxxxxxxx>
> > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> > ---
> >  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?

the major reason is to make the naming aligned since this patch
names the groups as KVM_DEV_VFIO_FILE.

> 
> 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.

hmmm, this way is clearer. I'd adopt it if it's acceptable.

> 
> 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?

legacy container/group path cannot do it as the below enhancement.
User needs to call KVM_DEV_VFIO_FILE before open devices, so this
should happen before _GET_DEVICE_FD. So the legacy path can never
pass device fds in KVM_DEV_VFIO_FILE.

https://lore.kernel.org/kvm/20230327102059.333d6976.alex.williamson@xxxxxxxxxx/#t

> > -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.

just as here. This means device fds can only be passed with KVM_DEV_VFIO_FILE
in the cdev path.

Regards,
Yi Liu

> > 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;
> >  		}





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