linux-kernel - Re: [PATCH v9 05/12] vfio: Introduce common function to add capabilities

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Date:   Tue, 25 Oct 2016 02:57:58 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.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 10/21/2016 12:54 AM, Alex Williamson wrote:
> 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.
> 

>From the code I see, we add one type of capability at a time, either
VFIO_REGION_INFO_CAP_SPARSE_MMAP or VFIO_REGION_INFO_CAP_TYPE. Both are
not the part of same case in the switch, right?
I do tested VFIO_REGION_INFO_CAP_SPARSE_MMAP by mapping some part of
BAR0 and that works.

Kirti.