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SubjectRe: [PATCH v1 5/8] vfio/type1: Report 1st-level/stage-1 format to userspace
On Sun, 22 Mar 2020 05:32:02 -0700
"Liu, Yi L" <yi.l.liu@intel.com> wrote:

> From: Liu Yi L <yi.l.liu@intel.com>
>
> VFIO exposes IOMMU nesting translation (a.k.a dual stage translation)
> capability to userspace. Thus applications like QEMU could support
> vIOMMU with hardware's nesting translation capability for pass-through
> devices. Before setting up nesting translation for pass-through devices,
> QEMU and other applications need to learn the supported 1st-lvl/stage-1
> translation structure format like page table format.
>
> Take vSVA (virtual Shared Virtual Addressing) as an example, to support
> vSVA for pass-through devices, QEMU setup nesting translation for pass-
> through devices. The guest page table are configured to host as 1st-lvl/
> stage-1 page table. Therefore, guest format should be compatible with
> host side.
>
> This patch reports the supported 1st-lvl/stage-1 page table format on the
> current platform to userspace. QEMU and other alike applications should
> use this format info when trying to setup IOMMU nesting translation on
> host IOMMU.
>
> Cc: Kevin Tian <kevin.tian@intel.com>
> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 56 +++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/vfio.h | 1 +
> 2 files changed, 57 insertions(+)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 9aa2a67..82a9e0b 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -2234,11 +2234,66 @@ static int vfio_iommu_type1_pasid_free(struct vfio_iommu *iommu,
> return ret;
> }
>
> +static int vfio_iommu_get_stage1_format(struct vfio_iommu *iommu,
> + u32 *stage1_format)
> +{
> + struct vfio_domain *domain;
> + u32 format = 0, tmp_format = 0;
> + int ret;
> +
> + mutex_lock(&iommu->lock);
> + if (list_empty(&iommu->domain_list)) {
> + mutex_unlock(&iommu->lock);
> + return -EINVAL;
> + }
> +
> + list_for_each_entry(domain, &iommu->domain_list, next) {
> + if (iommu_domain_get_attr(domain->domain,
> + DOMAIN_ATTR_PASID_FORMAT, &format)) {
> + ret = -EINVAL;
> + format = 0;
> + goto out_unlock;
> + }
> + /*
> + * format is always non-zero (the first format is
> + * IOMMU_PASID_FORMAT_INTEL_VTD which is 1). For
> + * the reason of potential different backed IOMMU
> + * formats, here we expect to have identical formats
> + * in the domain list, no mixed formats support.
> + * return -EINVAL to fail the attempt of setup
> + * VFIO_TYPE1_NESTING_IOMMU if non-identical formats
> + * are detected.
> + */
> + if (tmp_format && tmp_format != format) {
> + ret = -EINVAL;
> + format = 0;
> + goto out_unlock;
> + }
> +
> + tmp_format = format;
> + }
> + ret = 0;
> +
> +out_unlock:
> + if (format)
> + *stage1_format = format;
> + mutex_unlock(&iommu->lock);
> + return ret;
> +}
> +
> static int vfio_iommu_info_add_nesting_cap(struct vfio_iommu *iommu,
> struct vfio_info_cap *caps)
> {
> struct vfio_info_cap_header *header;
> struct vfio_iommu_type1_info_cap_nesting *nesting_cap;
> + u32 formats = 0;
> + int ret;
> +
> + ret = vfio_iommu_get_stage1_format(iommu, &formats);
> + if (ret) {
> + pr_warn("Failed to get stage-1 format\n");
> + return ret;

Looks like this generates a warning and causes the iommu_get_info ioctl
to fail if the hardware doesn't support the pasid format attribute, or
the domain list is empty. This breaks users on existing hardware.

> + }
>
> header = vfio_info_cap_add(caps, sizeof(*nesting_cap),
> VFIO_IOMMU_TYPE1_INFO_CAP_NESTING, 1);
> @@ -2254,6 +2309,7 @@ static int vfio_iommu_info_add_nesting_cap(struct vfio_iommu *iommu,
> /* nesting iommu type supports PASID requests (alloc/free) */
> nesting_cap->nesting_capabilities |= VFIO_IOMMU_PASID_REQS;
> }
> + nesting_cap->stage1_formats = formats;
>
> return 0;
> }
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index ed9881d..ebeaf3e 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -763,6 +763,7 @@ struct vfio_iommu_type1_info_cap_nesting {
> struct vfio_info_cap_header header;
> #define VFIO_IOMMU_PASID_REQS (1 << 0)
> __u32 nesting_capabilities;
> + __u32 stage1_formats;
> };
>
> #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)

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