Subject: [PATCH v9 7/7] vfio/type1: return MSI geometry through VFIO_IOMMU_GET_INFO capability chains

From: [email-masked] (Eric Auger)
Date: Tue, 10 May 2016 18:36:34 +0200

Hi Alex,
On 05/10/2016 12:49 AM, Alex Williamson wrote:
> On Wed,  4 May 2016 11:54:18 +0000
> Eric Auger <[email-masked]> wrote:
> 
>> This patch allows the user-space to retrieve the MSI geometry. The
>> implementation is based on capability chains, now also added to
>> VFIO_IOMMU_GET_INFO.
>>
>> The returned info comprise:
>> - whether the MSI IOVA are constrained to a reserved range (x86 case) and
>>   in the positive, the start/end of the aperture,
>> - or whether the IOVA aperture need to be set by the userspace. In that
>>   case, the size and alignment of the IOVA region to be provided are
>>   returned.
>>
>> In case the userspace must provide the IOVA range, we currently return
>> an arbitrary number of IOVA pages (16), supposed to fulfill the needs of
>> current ARM platforms. This may be deprecated by a more sophisticated
>> computation later on.
>>
>> Signed-off-by: Eric Auger <[email-masked]>
>>
>> ---
>> v8 -> v9:
>> - use iommu_msi_supported flag instead of programmable
>> - replace IOMMU_INFO_REQUIRE_MSI_MAP flag by a more sophisticated
>>   capability chain, reporting the MSI geometry
>>
>> v7 -> v8:
>> - use iommu_domain_msi_geometry
>>
>> v6 -> v7:
>> - remove the computation of the number of IOVA pages to be provisionned.
>>   This number depends on the domain/group/device topology which can
>>   dynamically change. Let's rely instead rely on an arbitrary max depending
>>   on the system
>>
>> v4 -> v5:
>> - move msi_info and ret declaration within the conditional code
>>
>> v3 -> v4:
>> - replace former vfio_domains_require_msi_mapping by
>>   more complex computation of MSI mapping requirements, especially the
>>   number of pages to be provided by the user-space.
>> - reword patch title
>>
>> RFC v1 -> v1:
>> - derived from
>>   [RFC PATCH 3/6] vfio: Extend iommu-info to return MSIs automap state
>> - renamed allow_msi_reconfig into require_msi_mapping
>> - fixed VFIO_IOMMU_GET_INFO
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 69 +++++++++++++++++++++++++++++++++++++++++
>>  include/uapi/linux/vfio.h       | 30 +++++++++++++++++-
>>  2 files changed, 98 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 2fc8197..841360b 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -1134,6 +1134,50 @@ static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
>>  	return ret;
>>  }
>>  
>> +static int compute_msi_geometry_caps(struct vfio_iommu *iommu,
>> +				     struct vfio_info_cap *caps)
>> +{
>> +	struct vfio_iommu_type1_info_cap_msi_geometry *vfio_msi_geometry;
>> +	struct iommu_domain_msi_geometry msi_geometry;
>> +	struct vfio_info_cap_header *header;
>> +	struct vfio_domain *d;
>> +	bool mapping_required;
>> +	size_t size;
>> +
>> +	mutex_lock(&iommu->lock);
>> +	/* All domains have same require_msi_map property, pick first */
>> +	d = list_first_entry(&iommu->domain_list, struct vfio_domain, next);
>> +	iommu_domain_get_attr(d->domain, DOMAIN_ATTR_MSI_GEOMETRY,
>> +			      &msi_geometry);
>> +	mapping_required = msi_geometry.iommu_msi_supported;
>> +
>> +	mutex_unlock(&iommu->lock);
>> +
>> +	size = sizeof(*vfio_msi_geometry);
>> +	header = vfio_info_cap_add(caps, size,
>> +				   VFIO_IOMMU_TYPE1_INFO_CAP_MSI_GEOMETRY, 1);
>> +
>> +	if (IS_ERR(header))
>> +		return PTR_ERR(header);
>> +
>> +	vfio_msi_geometry = container_of(header,
>> +				struct vfio_iommu_type1_info_cap_msi_geometry,
>> +				header);
>> +
>> +	vfio_msi_geometry->reserved = !mapping_required;
>> +	if (vfio_msi_geometry->reserved) {
>> +		vfio_msi_geometry->aperture_start = msi_geometry.aperture_start;
>> +		vfio_msi_geometry->aperture_end = msi_geometry.aperture_end;
>> +		return 0;
>> +	}
>> +
>> +	vfio_msi_geometry->alignment = 1 << __ffs(vfio_pgsize_bitmap(iommu));
>> +	/* we currently report the need for an arbitray number of 16 pages */
>> +	vfio_msi_geometry->size = 16 * vfio_msi_geometry->alignment;
> 
> Hmm, that really is arbitrary.  How could we know a real value here?
Yes I fully agree and this is aknowledged in the cover/commit msg. I
dared to do that because this has the benefits to allow introducing the
userspace API while refining this computation later on.

I did not find yet an elegant solution to compute the platform max
number/size of doorbells (besides what I did in the past which was
dependent on the group/device current topology).

Maybe an option would be to have the relevant MSI controllers
registering their doorbells in a global list at probe time and then we
would enumerate all of them. I was reluctant to add this new
functionality in the series at this stage, hence the current simplification.
> 
>> +
>> +	return 0;
>> +}
>> +
>>  static long vfio_iommu_type1_ioctl(void *iommu_data,
>>  				   unsigned int cmd, unsigned long arg)
>>  {
>> @@ -1155,6 +1199,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>  		}
>>  	} else if (cmd == VFIO_IOMMU_GET_INFO) {
>>  		struct vfio_iommu_type1_info info;
>> +		struct vfio_info_cap caps = { .buf = NULL, .size = 0 };
>> +		int ret;
>>  
>>  		minsz = offsetofend(struct vfio_iommu_type1_info, iova_pgsizes);
>>  
>> @@ -1168,6 +1214,29 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>  
>>  		info.iova_pgsizes = vfio_pgsize_bitmap(iommu);
>>  
>> +		ret = compute_msi_geometry_caps(iommu, &caps);
>> +		if (ret)
>> +			return ret;
>> +
>> +		if (caps.size) {
>> +			info.flags |= VFIO_IOMMU_INFO_CAPS;
>> +			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));
>> +				if (copy_to_user((void __user *)arg +
>> +						sizeof(info), caps.buf,
>> +						caps.size)) {
>> +					kfree(caps.buf);
>> +					return -EFAULT;
>> +				}
>> +				info.cap_offset = sizeof(info);
>> +			}
>> +
>> +			kfree(caps.buf);
>> +		}
>> +
>>  		return copy_to_user((void __user *)arg, &info, minsz) ?
>>  			-EFAULT : 0;
>>  
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index 4a9dbc2..0ff6a8d 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -488,7 +488,33 @@ struct vfio_iommu_type1_info {
>>  	__u32	argsz;
>>  	__u32	flags;
>>  #define VFIO_IOMMU_INFO_PGSIZES (1 << 0)	/* supported page sizes info */
>> -	__u64	iova_pgsizes;		/* Bitmap of supported page sizes */
>> +#define VFIO_IOMMU_INFO_CAPS	(1 << 1)	/* Info supports caps */
>> +	__u32   cap_offset;	/* Offset within info struct of first cap */
>> +	__u64	iova_pgsizes;	/* Bitmap of supported page sizes */
> 
> This would break existing users, we can't arbitrarily change the offset
> of iova_pgsizes.  We can add cap_offset to the end and I think
> everything would work about above if we do that.
Hum yes, sorry for the lack of care.
> 
>> +};
>> +
>> +#define VFIO_IOMMU_TYPE1_INFO_CAP_MSI_GEOMETRY	1
>> +
>> +/*
>> + * The MSI geometry capability allows to report the MSI IOVA geometry:
>> + * - either the MSI IOVAs are constrained within a reserved IOVA aperture
>> + *   whose boundaries are given by [@aperture_start, @aperture_end].
>> + *   this is typically the case on x86 host. The userspace is not allowed
>> + *   to map userspace memory at IOVAs intersecting this range using
>> + *   VFIO_IOMMU_MAP_DMA.
>> + * - or the MSI IOVAs are not requested to belong to any reserved range;
>> + *   in that case the userspace must provide an IOVA window characterized by
>> + *   @size and @alignment using VFIO_IOMMU_MAP_DMA with RESERVED_MSI_IOVA flag.
>> + */
>> +struct vfio_iommu_type1_info_cap_msi_geometry {
>> +	struct vfio_info_cap_header header;
>> +	bool reserved; /* Are MSI IOVAs within a reserved aperture? */
> 
> Do bools have a guaranteed user size?  Let's make this a __u32 and call
> it flags with bit 0 defined as reserved.  I'm tempted to suggest we
> could figure out how to make alignment fit in another __u32 so we have a
> properly packed structure, otherwise we should make a reserved __u32.
OK will rewrite & check that.

Thanks

Eric
> 
>> +	/* reserved */
>> +	__u64 aperture_start;
>> +	__u64 aperture_end;
>> +	/* not reserved */
>> +	__u64 size; /* IOVA aperture size in bytes the userspace must provide */
>> +	__u64 alignment; /* alignment of the window, in bytes */
>>  };
>>  
>>  #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
>> @@ -503,6 +529,8 @@ struct vfio_iommu_type1_info {
>>   * IOVA region that will be used on some platforms to map the host MSI frames.
>>   * In that specific case, vaddr is ignored. Once registered, an MSI reserved
>>   * IOVA region stays until the container is closed.
>> + * The requirement for provisioning such reserved IOVA range can be checked by
>> + * checking the VFIO_IOMMU_TYPE1_INFO_CAP_MSI_GEOMETRY capability.
>>   */
>>  struct vfio_iommu_type1_dma_map {
>>  	__u32	argsz;
>