Re: [PATCH] vfio: Simplify capability helper

[Zhenyu Wang <zhenyuw@linux.intel.com>]

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On 2017.12.13 12:13:34 +1100, Alexey Kardashevskiy wrote:
> On 13/12/17 06:59, Alex Williamson wrote:
> > The vfio_info_add_capability() helper requires the caller to pass a
> > capability ID, which it then uses to fill in header fields, assuming
> > hard coded versions.  This makes for an awkward and rigid interface.
> > The only thing we want this helper to do is allocate sufficient
> > space in the caps buffer and chain this capability into the list.
> > Reduce it to that simple task.
> > 
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> 
> 
> Makes more sense now, thanks. I'll repost mine on top of this.
> 
> 
> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> 
>

Looks good for KVMGT part.

Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>

> Below one observation, unrelated to this patch.
> 
> > ---
> >  drivers/gpu/drm/i915/gvt/kvmgt.c |   15 +++++++----
> >  drivers/vfio/pci/vfio_pci.c      |   14 ++++++----
> >  drivers/vfio/vfio.c              |   52 +++-----------------------------------
> >  include/linux/vfio.h             |    3 +-
> >  4 files changed, 24 insertions(+), 60 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> > index 96060920a6fe..0a7d084da1a2 100644
> > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> > @@ -1012,6 +1012,8 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
> >  			if (!sparse)
> >  				return -ENOMEM;
> >  
> > +			sparse->header.id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
> > +			sparse->header.version = 1;
> >  			sparse->nr_areas = nr_areas;
> >  			cap_type_id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
> 
> 
> @cap_type_id is initialized in just one of many cases of switch
> (info.index) and after the entire switch, there is switch (cap_type_id). I
> wonder why compiler missed "potentially uninitialized variable here,
> although there is no bug - @cap_type_id is in sync with @spapse. It would
> make it cleaner imho just to have vfio_info_add_capability() next to the
> header initialization.
> 

yeah, we could clean that up, thanks for pointing out.

> 
> 
> >  			sparse->areas[0].offset =
> > @@ -1033,7 +1035,9 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
> >  			break;
> >  		default:
> >  			{
> > -				struct vfio_region_info_cap_type cap_type;
> > +				struct vfio_region_info_cap_type cap_type = {
> > +					.header.id = VFIO_REGION_INFO_CAP_TYPE,
> > +					.header.version = 1 };
> >  
> >  				if (info.index >= VFIO_PCI_NUM_REGIONS +
> >  						vgpu->vdev.num_regions)
> > @@ -1050,8 +1054,8 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
> >  				cap_type.subtype = vgpu->vdev.region[i].subtype;
> >  
> >  				ret = vfio_info_add_capability(&caps,
> > -						VFIO_REGION_INFO_CAP_TYPE,
> > -						&cap_type);
> > +							&cap_type.header,
> > +							sizeof(cap_type));
> >  				if (ret)
> >  					return ret;
> >  			}
> > @@ -1061,8 +1065,9 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
> >  			switch (cap_type_id) {
> >  			case VFIO_REGION_INFO_CAP_SPARSE_MMAP:
> >  				ret = vfio_info_add_capability(&caps,
> > -					VFIO_REGION_INFO_CAP_SPARSE_MMAP,
> > -					sparse);
> > +					&sparse->header, sizeof(*sparse) +
> > +					(sparse->nr_areas *
> > +						sizeof(*sparse->areas)));
> >  				kfree(sparse);
> >  				if (ret)
> >  					return ret;
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index f041b1a6cf66..a73e40983880 100644
> > --- a/drivers/vfio/pci/vfio_pci.c
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -582,6 +582,8 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
> >  	if (!sparse)
> >  		return -ENOMEM;
> >  
> > +	sparse->header.id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
> > +	sparse->header.version = 1;
> >  	sparse->nr_areas = nr_areas;
> >  
> >  	if (vdev->msix_offset & PAGE_MASK) {
> > @@ -597,8 +599,7 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
> >  		i++;
> >  	}
> >  
> > -	ret = vfio_info_add_capability(caps, VFIO_REGION_INFO_CAP_SPARSE_MMAP,
> > -				       sparse);
> > +	ret = vfio_info_add_capability(caps, &sparse->header, size);
> >  	kfree(sparse);
> >  
> >  	return ret;
> > @@ -741,7 +742,9 @@ static long vfio_pci_ioctl(void *device_data,
> >  			break;
> >  		default:
> >  		{
> > -			struct vfio_region_info_cap_type cap_type;
> > +			struct vfio_region_info_cap_type cap_type = {
> > +					.header.id = VFIO_REGION_INFO_CAP_TYPE,
> > +					.header.version = 1 };
> >  
> >  			if (info.index >=
> >  			    VFIO_PCI_NUM_REGIONS + vdev->num_regions)
> > @@ -756,9 +759,8 @@ static long vfio_pci_ioctl(void *device_data,
> >  			cap_type.type = vdev->region[i].type;
> >  			cap_type.subtype = vdev->region[i].subtype;
> >  
> > -			ret = vfio_info_add_capability(&caps,
> > -						      VFIO_REGION_INFO_CAP_TYPE,
> > -						      &cap_type);
> > +			ret = vfio_info_add_capability(&caps, &cap_type.header,
> > +						       sizeof(cap_type));
> >  			if (ret)
> >  				return ret;
> >  
> > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> > index 2bc3705a99bd..721f97f8dac1 100644
> > --- a/drivers/vfio/vfio.c
> > +++ b/drivers/vfio/vfio.c
> > @@ -1857,63 +1857,19 @@ void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset)
> >  }
> >  EXPORT_SYMBOL(vfio_info_cap_shift);
> >  
> > -static int sparse_mmap_cap(struct vfio_info_cap *caps, void *cap_type)
> > +int vfio_info_add_capability(struct vfio_info_cap *caps,
> > +			     struct vfio_info_cap_header *cap, size_t size)
> >  {
> >  	struct vfio_info_cap_header *header;
> > -	struct vfio_region_info_cap_sparse_mmap *sparse_cap, *sparse = cap_type;
> > -	size_t size;
> >  
> > -	size = sizeof(*sparse) + sparse->nr_areas *  sizeof(*sparse->areas);
> > -	header = vfio_info_cap_add(caps, size,
> > -				   VFIO_REGION_INFO_CAP_SPARSE_MMAP, 1);
> > +	header = vfio_info_cap_add(caps, size, cap->id, cap->version);
> >  	if (IS_ERR(header))
> >  		return PTR_ERR(header);
> >  
> > -	sparse_cap = container_of(header,
> > -			struct vfio_region_info_cap_sparse_mmap, header);
> > -	sparse_cap->nr_areas = sparse->nr_areas;
> > -	memcpy(sparse_cap->areas, sparse->areas,
> > -	       sparse->nr_areas * sizeof(*sparse->areas));
> > -	return 0;
> > -}
> > -
> > -static int region_type_cap(struct vfio_info_cap *caps, void *cap_type)
> > -{
> > -	struct vfio_info_cap_header *header;
> > -	struct vfio_region_info_cap_type *type_cap, *cap = cap_type;
> > +	memcpy(header + 1, cap + 1, size - sizeof(*header));
> >  
> > -	header = vfio_info_cap_add(caps, sizeof(*cap),
> > -				   VFIO_REGION_INFO_CAP_TYPE, 1);
> > -	if (IS_ERR(header))
> > -		return PTR_ERR(header);
> > -
> > -	type_cap = container_of(header, struct vfio_region_info_cap_type,
> > -				header);
> > -	type_cap->type = cap->type;
> > -	type_cap->subtype = cap->subtype;
> >  	return 0;
> >  }
> > -
> > -int vfio_info_add_capability(struct vfio_info_cap *caps, int cap_type_id,
> > -			     void *cap_type)
> > -{
> > -	int ret = -EINVAL;
> > -
> > -	if (!cap_type)
> > -		return 0;
> > -
> > -	switch (cap_type_id) {
> > -	case VFIO_REGION_INFO_CAP_SPARSE_MMAP:
> > -		ret = sparse_mmap_cap(caps, cap_type);
> > -		break;
> > -
> > -	case VFIO_REGION_INFO_CAP_TYPE:
> > -		ret = region_type_cap(caps, cap_type);
> > -		break;
> > -	}
> > -
> > -	return ret;
> > -}
> >  EXPORT_SYMBOL(vfio_info_add_capability);
> >  
> >  int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr, int num_irqs,
> > diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> > index a47b985341d1..66741ab087c1 100644
> > --- a/include/linux/vfio.h
> > +++ b/include/linux/vfio.h
> > @@ -145,7 +145,8 @@ extern struct vfio_info_cap_header *vfio_info_cap_add(
> >  extern void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset);
> >  
> >  extern int vfio_info_add_capability(struct vfio_info_cap *caps,
> > -				    int cap_type_id, void *cap_type);
> > +				    struct vfio_info_cap_header *cap,
> > +				    size_t size);
> >  
> >  extern int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr,
> >  					      int num_irqs, int max_irq_type,
> > 
> 
> 
> -- 
> Alexey

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