Re: [PATCH v13 15/15] vfio/type1: Return the MSI geometry through VFIO_IOMMU_GET_INFO capability chains

[Alex Williamson]

On Thu, 6 Oct 2016 14:20:40 -0600
Alex Williamson <alex.williamson@xxxxxxxxxx> wrote:

> On Thu,  6 Oct 2016 08:45:31 +0000
> Eric Auger <eric.auger@xxxxxxxxxx> 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 window to be provided are
> >   returned.
> > 
> > In case the userspace must provide the IOVA aperture, we currently report
> > a size/alignment based on all the doorbells registered by the host kernel.
> > This may exceed the actual needs.
> > 
> > Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> > 
> > ---
> > v11 -> v11:
> > - msi_doorbell_pages was renamed msi_doorbell_calc_pages
> > 
> > v9 -> v10:
> > - move cap_offset after iova_pgsizes
> > - replace __u64 alignment by __u32 order
> > - introduce __u32 flags in vfio_iommu_type1_info_cap_msi_geometry and
> >   fix alignment
> > - call msi-doorbell API to compute the size/alignment
> > 
> > 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 | 78 ++++++++++++++++++++++++++++++++++++++++-
> >  include/uapi/linux/vfio.h       | 32 ++++++++++++++++-
> >  2 files changed, 108 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index dc3ee5d..ce5e7eb 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -38,6 +38,8 @@
> >  #include <linux/workqueue.h>
> >  #include <linux/dma-iommu.h>
> >  #include <linux/msi-doorbell.h>
> > +#include <linux/irqdomain.h>
> > +#include <linux/msi.h>
> >  
> >  #define DRIVER_VERSION  "0.2"
> >  #define DRIVER_AUTHOR   "Alex Williamson <alex.williamson@xxxxxxxxxx>"
> > @@ -1101,6 +1103,55 @@ 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;
> > +	unsigned long order = __ffs(vfio_pgsize_bitmap(iommu));
> > +	struct iommu_domain_msi_geometry msi_geometry;
> > +	struct vfio_info_cap_header *header;
> > +	struct vfio_domain *d;
> > +	bool reserved;
> > +	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);
> > +	reserved = !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->flags = reserved;  
> 
> Use the bit flag VFIO_IOMMU_MSI_GEOMETRY_RESERVED
> 
> > +	if (reserved) {
> > +		vfio_msi_geometry->aperture_start = msi_geometry.aperture_start;
> > +		vfio_msi_geometry->aperture_end = msi_geometry.aperture_end;  
> 
> But maybe nobody has set these, did you intend to use
> iommu_domain_msi_aperture_valid(), which you defined early on but never
> used?
> 
> > +		return 0;
> > +	}
> > +
> > +	vfio_msi_geometry->order = order;  
> 
> I'm tempted to suggest that a user could do the same math on their own
> since we provide the supported bitmap already... could it ever not be
> the same? 
> 
> > +	/*
> > +	 * we compute a system-wide requirement based on all the registered
> > +	 * doorbells
> > +	 */
> > +	vfio_msi_geometry->size =
> > +		msi_doorbell_calc_pages(order) * ((uint64_t) 1 << order);
> > +
> > +	return 0;
> > +}
> > +
> >  static long vfio_iommu_type1_ioctl(void *iommu_data,
> >  				   unsigned int cmd, unsigned long arg)
> >  {
> > @@ -1122,8 +1173,10 @@ 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);
> > +		minsz = offsetofend(struct vfio_iommu_type1_info, cap_offset);
> >  
> >  		if (copy_from_user(&info, (void __user *)arg, minsz))
> >  			return -EFAULT;
> > @@ -1135,6 +1188,29 @@ 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..8dae013 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -488,7 +488,35 @@ 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 */
> > +	__u64	iova_pgsizes;	/* Bitmap of supported page sizes */
> > +	__u32	__resv;
> > +	__u32   cap_offset;	/* Offset within info struct of first cap */
> > +};  
> 
> I understand the padding, but not the ordering.  Why not end with
> padding?
> 
> > +
> > +#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;
> > +	__u32 flags;
> > +#define VFIO_IOMMU_MSI_GEOMETRY_RESERVED (1 << 0) /* reserved geometry */
> > +	/* not reserved */
> > +	__u32 order; /* iommu page order used for aperture alignment*/
> > +	__u64 size; /* IOVA aperture size (bytes) the userspace must provide */
> > +	/* reserved */
> > +	__u64 aperture_start;
> > +	__u64 aperture_end;  
> 
> Should these be a union?  We never set them both.  Should the !reserved
> case have a flag as well, so the user can positively identify what's
> being provided?

Actually, is there really any need to fit both of these within the same
structure?  Part of the idea of the capability chains is we can create
a capability for each new thing we want to describe.  So, we could
simply define a generic reserved IOVA range capability with a 'start'
and 'end' and then another capability to define MSI mapping
requirements.  Thanks,

Alex
 
> >  };
> >  
> >  #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
> > @@ -503,6 +531,8 @@ 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;  
>