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SubjectRe: [PATCH v9 7/7] vfio/type1: return MSI geometry through VFIO_IOMMU_GET_INFO capability chains
On Wed,  4 May 2016 11:54:18 +0000
Eric Auger <eric.auger@linaro.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 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 <eric.auger@linaro.org>
>
> ---
> 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?

> +
> + 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.

> +};
> +
> +#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.

> + /* 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;

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