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

Alex Williamson
2016-10-06T20:42:51Z

On Thu, 6 Oct 2016 14:20:40 -0600
Alex Williamson <alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:

> On Thu, 6 Oct 2016 08:45:31 +0000
> Eric Auger <eric.auger-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 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-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> >
> > ---
> > 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-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>"
> > @@ -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;
>