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Date:   Thu, 20 Oct 2016 13:24:52 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Kirti Wankhede <kwankhede@...dia.com>
Cc:     <pbonzini@...hat.com>, <kraxel@...hat.com>, <cjia@...dia.com>,
        <qemu-devel@...gnu.org>, <kvm@...r.kernel.org>,
        <kevin.tian@...el.com>, <jike.song@...el.com>,
        <bjsdjshi@...ux.vnet.ibm.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 05/12] vfio: Introduce common function to add
 capabilities

On Tue, 18 Oct 2016 02:52:05 +0530
Kirti Wankhede <kwankhede@...dia.com> wrote:

> Vendor driver using mediated device framework should use
> vfio_info_add_capability() to add capabilities.
> Introduced this function to reduce code duplication in vendor drivers.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@...dia.com>
> Signed-off-by: Neo Jia <cjia@...dia.com>
> Change-Id: I6fca329fa2291f37a2c859d0bc97574d9e2ce1a6
> ---
>  drivers/vfio/vfio.c  | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/vfio.h |  4 +++
>  2 files changed, 82 insertions(+)
> 
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index a5a210005b65..e96cb3f7a23c 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1799,6 +1799,84 @@ void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset)
>  }
>  EXPORT_SYMBOL_GPL(vfio_info_cap_shift);
>  
> +static int sparse_mmap_cap(struct vfio_info_cap *caps, void *cap_type)
> +{
> +	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);
> +	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;
> +
> +	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_region_info *info,
> +			     struct vfio_info_cap *caps,
> +			     int cap_type_id,
> +			     void *cap_type)
> +{
> +	int ret;
> +
> +	if (!cap_type)
> +		return 0;
> +
> +	switch (cap_type_id) {
> +	case VFIO_REGION_INFO_CAP_SPARSE_MMAP:
> +		ret = sparse_mmap_cap(caps, cap_type);
> +		if (ret)
> +			return ret;
> +		break;
> +
> +	case VFIO_REGION_INFO_CAP_TYPE:
> +		ret = region_type_cap(caps, cap_type);
> +		if (ret)
> +			return ret;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	info->flags |= VFIO_REGION_INFO_FLAG_CAPS;
> +
> +	if (caps->size) {
> +		if (info->argsz < sizeof(*info) + caps->size) {
> +			info->argsz = sizeof(*info) + caps->size;
> +			info->cap_offset = 0;
> +		} else {
> +			vfio_info_cap_shift(caps, sizeof(*info));
> +			info->cap_offset = sizeof(*info);

This doesn't work.  We build the capability chain in a buffer and
vfio_info_cap_add() expects the chain to be zero-based as each
capability is added.  vfio_info_cap_shift() is meant to be called once
on that buffer immediately before copying it back to the user buffer to
adjust the chain offsets to account for the offset within the buffer.
vfio_info_cap_shift() cannot be called repeatedly on the buffer as we
do support multiple capabilities in a chain.

> +		}
> +	}
> +	return 0;
> +}
> +EXPORT_SYMBOL(vfio_info_add_capability);
> +
>  
>  /*
>   * Pin a set of guest PFNs and return their associated host PFNs for
> local diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 0bd25ba6223d..854a4b40be02 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -108,6 +108,10 @@ extern struct vfio_info_cap_header
> *vfio_info_cap_add( struct vfio_info_cap *caps, size_t size, u16 id,
> u16 version); extern void vfio_info_cap_shift(struct vfio_info_cap
> *caps, size_t offset); 
> +extern int vfio_info_add_capability(struct vfio_region_info *info,
> +				    struct vfio_info_cap *caps,
> +				    int cap_type_id, void *cap_type);
> +
>  struct pci_dev;
>  #ifdef CONFIG_EEH
>  extern void vfio_spapr_pci_eeh_open(struct pci_dev *pdev);

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