On Thu, 30 Nov 2017 12:34:38 +0100
Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx> wrote:
> When userland VFIO defines a new IOMMU for a guest it may
> want to specify to the guest the physical limits of
> the underlying host IOMMU to avoid access to forbidden
> memory ranges.
>
> Currently, the vfio_iommu_type1 driver does not report this
> information to userland.
>
> Let's extend the vfio_iommu_type1_info structure reported
> by the ioctl VFIO_IOMMU_GET_INFO command to report the
> IOMMU limits as new uint64_t entries aperture_start and
> aperture_end.
>
> Let's also extend the flags bit map to add a flag specifying
> if this extension of the info structure is reported or not.
>
> Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/vfio/vfio_iommu_type1.c | 42 +++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/vfio.h | 3 +++
> 2 files changed, 45 insertions(+)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 8549cb1..7da5fe0 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -1526,6 +1526,40 @@ static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
> return ret;
> }
>
> +/**
> + * vfio_get_aperture - report minimal aperture of a vfio_iommu
> + * @iommu: the current vfio_iommu
> + * @start: a pointer to the aperture start
> + * @end : a pointer to the aperture end
> + *
> + * This function iterate on the domains using the given vfio_iommu
> + * and restrict the aperture to the minimal aperture common
> + * to all domains sharing this vfio_iommu.
> + */
> +static void vfio_get_aperture(struct vfio_iommu *iommu, uint64_t *start,
> + uint64_t *end)
> +{
> + struct iommu_domain_geometry geometry;
> + struct vfio_domain *domain;
> +
> + *start = 0;
> + *end = U64_MAX;
> +
> + mutex_lock(&iommu->lock);
> + /* loop on all domains using this vfio_iommu */
> + list_for_each_entry(domain, &iommu->domain_list, next) {
> + iommu_domain_get_attr(domain->domain, DOMAIN_ATTR_GEOMETRY,
> + &geometry);
> + if (geometry.force_aperture) {
> + if (geometry.aperture_start > *start)
> + *start = geometry.aperture_start;
> + if (geometry.aperture_end < *end)
> + *end = geometry.aperture_end;
> + }
> + }
> + mutex_unlock(&iommu->lock);
> +}
> +
> static long vfio_iommu_type1_ioctl(void *iommu_data,
> unsigned int cmd, unsigned long arg)
> {
> @@ -1560,6 +1594,14 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>
> info.iova_pgsizes = vfio_pgsize_bitmap(iommu);
>
> + minsz = min_t(size_t, info.argsz, sizeof(info));
> + if (minsz >= offsetofend(struct vfio_iommu_type1_info,
> + aperture_end)) {
> + info.flags |= VFIO_IOMMU_INFO_APERTURE;
> + vfio_get_aperture(iommu, &info.aperture_start,
> + &info.aperture_end);
> + }
> +
> 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 0fb25fb..780d909 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -519,6 +519,9 @@ struct vfio_iommu_type1_info {
> __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_APERTURE (1 << 1) /* supported aperture info */
> + __u64 aperture_start; /* start of DMA aperture */
> + __u64 aperture_end; /* end of DMA aperture */
> };
>
> #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
This only supports the most simple topology, even x86 cannot claim to
have a single contiguous aperture, it's typically bisected by an MSI
window. I think we need an API that supports one or more apertures
out of the box. Also as Eric indicates, a capability is probably the
better option for creating a flexible structure. Thanks,
Alex
