Re: [PATCH v6 04/15] vfio/type1: Report iommu nesting info to userspace

Alex Williamson
2020-08-20T19:52:23Z

On Mon, 27 Jul 2020 23:27:33 -0700
Liu Yi L <yi.l.liu@intel.com> wrote:

> This patch exports iommu nesting capability info to user space through
> VFIO. Userspace is expected to check this info for supported uAPIs (e.g.
> PASID alloc/free, bind page table, and cache invalidation) and the vendor
> specific format information for first level/stage page table that will be
> bound to.
>
> The nesting info is available only after container set to be NESTED type.
> Current implementation imposes one limitation - one nesting container
> should include at most one iommu group. The philosophy of vfio container
> is having all groups/devices within the container share the same IOMMU
> context. When vSVA is enabled, one IOMMU context could include one 2nd-
> level address space and multiple 1st-level address spaces. While the
> 2nd-level address space is reasonably sharable by multiple groups, blindly
> sharing 1st-level address spaces across all groups within the container
> might instead break the guest expectation. In the future sub/super container
> concept might be introduced to allow partial address space sharing within
> an IOMMU context. But for now let's go with this restriction by requiring
> singleton container for using nesting iommu features. Below link has the
> related discussion about this decision.
>
> https://lore.kernel.org/kvm/20200515115924.37e6996d@w520.home/
>
> This patch also changes the NESTING type container behaviour. Something
> that would have succeeded before will now fail: Before this series, if
> user asked for a VFIO_IOMMU_TYPE1_NESTING, it would have succeeded even
> if the SMMU didn't support stage-2, as the driver would have silently
> fallen back on stage-1 mappings (which work exactly the same as stage-2
> only since there was no nesting supported). After the series, we do check
> for DOMAIN_ATTR_NESTING so if user asks for VFIO_IOMMU_TYPE1_NESTING and
> the SMMU doesn't support stage-2, the ioctl fails. But it should be a good
> fix and completely harmless. Detail can be found in below link as well.
>
> https://lore.kernel.org/kvm/20200717090900.GC4850@myrica/
>
> 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>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> ---
> v5 -> v6:
> *) address comments against v5 from Eric Auger.
> *) don't report nesting cap to userspace if the nesting_info->format is
> invalid.
>
> v4 -> v5:
> *) address comments from Eric Auger.
> *) return struct iommu_nesting_info for VFIO_IOMMU_TYPE1_INFO_CAP_NESTING as
> cap is much "cheap", if needs extension in future, just define another cap.
> https://lore.kernel.org/kvm/20200708132947.5b7ee954@x1.home/
>
> v3 -> v4:
> *) address comments against v3.
>
> v1 -> v2:
> *) added in v2
> ---
> drivers/vfio/vfio_iommu_type1.c | 106 +++++++++++++++++++++++++++++++++++-----
> include/uapi/linux/vfio.h | 19 +++++++
> 2 files changed, 113 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 3bd70ff..18ff0c3 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -62,18 +62,20 @@ MODULE_PARM_DESC(dma_entry_limit,
> "Maximum number of user DMA mappings per container (65535).");
>
> struct vfio_iommu {
> - struct list_head domain_list;
> - struct list_head iova_list;
> - struct vfio_domain *external_domain; /* domain for external user */
> - struct mutex lock;
> - struct rb_root dma_list;
> - struct blocking_notifier_head notifier;
> - unsigned int dma_avail;
> - uint64_t pgsize_bitmap;
> - bool v2;
> - bool nesting;
> - bool dirty_page_tracking;
> - bool pinned_page_dirty_scope;
> + struct list_head domain_list;
> + struct list_head iova_list;
> + /* domain for external user */
> + struct vfio_domain *external_domain;
> + struct mutex lock;
> + struct rb_root dma_list;
> + struct blocking_notifier_head notifier;
> + unsigned int dma_avail;
> + uint64_t pgsize_bitmap;
> + bool v2;
> + bool nesting;
> + bool dirty_page_tracking;
> + bool pinned_page_dirty_scope;
> + struct iommu_nesting_info *nesting_info;
> };
>
> struct vfio_domain {
> @@ -130,6 +132,9 @@ struct vfio_regions {
> #define IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu) \
> (!list_empty(&iommu->domain_list))
>
> +#define CONTAINER_HAS_DOMAIN(iommu) (((iommu)->external_domain) || \
> + (!list_empty(&(iommu)->domain_list)))
> +
> #define DIRTY_BITMAP_BYTES(n) (ALIGN(n, BITS_PER_TYPE(u64)) / BITS_PER_BYTE)
>
> /*
> @@ -1929,6 +1934,13 @@ static void vfio_iommu_iova_insert_copy(struct vfio_iommu *iommu,
>
> list_splice_tail(iova_copy, iova);
> }
> +
> +static void vfio_iommu_release_nesting_info(struct vfio_iommu *iommu)
> +{
> + kfree(iommu->nesting_info);
> + iommu->nesting_info = NULL;
> +}
> +
> static int vfio_iommu_type1_attach_group(void *iommu_data,
> struct iommu_group *iommu_group)
> {
> @@ -1959,6 +1971,12 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
> }
> }
>
> + /* Nesting type container can include only one group */
> + if (iommu->nesting && CONTAINER_HAS_DOMAIN(iommu)) {
> + mutex_unlock(&iommu->lock);
> + return -EINVAL;
> + }
> +
> group = kzalloc(sizeof(*group), GFP_KERNEL);
> domain = kzalloc(sizeof(*domain), GFP_KERNEL);
> if (!group || !domain) {
> @@ -2029,6 +2047,32 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
> if (ret)
> goto out_domain;

I think that currently a user can configure a VFIO_TYPE1_NESTING_IOMMU
IOMMU type with a non-IOMMU backed mdev. Does that make any sort of
sense or is this a bug? Thanks,

Alex

>
> + /* Nesting cap info is available only after attaching */
> + if (iommu->nesting) {
> + struct iommu_nesting_info tmp = { .argsz = 0, };
> +
> + /* First get the size of vendor specific nesting info */
> + ret = iommu_domain_get_attr(domain->domain,
> + DOMAIN_ATTR_NESTING,
> + &tmp);
> + if (ret)
> + goto out_detach;
> +
> + iommu->nesting_info = kzalloc(tmp.argsz, GFP_KERNEL);
> + if (!iommu->nesting_info) {
> + ret = -ENOMEM;
> + goto out_detach;
> + }
> +
> + /* Now get the nesting info */
> + iommu->nesting_info->argsz = tmp.argsz;
> + ret = iommu_domain_get_attr(domain->domain,
> + DOMAIN_ATTR_NESTING,
> + iommu->nesting_info);
> + if (ret)
> + goto out_detach;
> + }
> +
> /* Get aperture info */
> iommu_domain_get_attr(domain->domain, DOMAIN_ATTR_GEOMETRY, &geo);
>
> @@ -2138,6 +2182,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
> return 0;
>
> out_detach:
> + vfio_iommu_release_nesting_info(iommu);
> vfio_iommu_detach_group(domain, group);
> out_domain:
> iommu_domain_free(domain->domain);
> @@ -2338,6 +2383,8 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
> vfio_iommu_unmap_unpin_all(iommu);
> else
> vfio_iommu_unmap_unpin_reaccount(iommu);
> +
> + vfio_iommu_release_nesting_info(iommu);
> }
> iommu_domain_free(domain->domain);
> list_del(&domain->next);
> @@ -2546,6 +2593,39 @@ static int vfio_iommu_migration_build_caps(struct vfio_iommu *iommu,
> return vfio_info_add_capability(caps, &cap_mig.header, sizeof(cap_mig));
> }
>
> +static int vfio_iommu_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;
> + size_t size;
> +
> + /* when nesting_info is null, no need go further */
> + if (!iommu->nesting_info)
> + return 0;
> +
> + /* when @format of nesting_info is 0, fail the call */
> + if (iommu->nesting_info->format == 0)
> + return -ENOENT;
> +
> + size = offsetof(struct vfio_iommu_type1_info_cap_nesting, info) +
> + iommu->nesting_info->argsz;
> +
> + header = vfio_info_cap_add(caps, size,
> + VFIO_IOMMU_TYPE1_INFO_CAP_NESTING, 1);
> + if (IS_ERR(header))
> + return PTR_ERR(header);
> +
> + nesting_cap = container_of(header,
> + struct vfio_iommu_type1_info_cap_nesting,
> + header);
> +
> + memcpy(&nesting_cap->info, iommu->nesting_info,
> + iommu->nesting_info->argsz);
> +
> + return 0;
> +}
> +
> static int vfio_iommu_type1_get_info(struct vfio_iommu *iommu,
> unsigned long arg)
> {
> @@ -2581,6 +2661,8 @@ static int vfio_iommu_type1_get_info(struct vfio_iommu *iommu,
> if (!ret)
> ret = vfio_iommu_iova_build_caps(iommu, &caps);
>
> + ret = vfio_iommu_add_nesting_cap(iommu, &caps);
> +
> mutex_unlock(&iommu->lock);
>
> if (ret)
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 9204705..0cf3d6d 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -14,6 +14,7 @@
>
> #include <linux/types.h>
> #include <linux/ioctl.h>
> +#include <linux/iommu.h>
>
> #define VFIO_API_VERSION 0
>
> @@ -1039,6 +1040,24 @@ struct vfio_iommu_type1_info_cap_migration {
> __u64 max_dirty_bitmap_size; /* in bytes */
> };
>
> +/*
> + * The nesting capability allows to report the related capability
> + * and info for nesting iommu type.
> + *
> + * The structures below define version 1 of this capability.
> + *
> + * Userspace selected VFIO_TYPE1_NESTING_IOMMU type should check
> + * this capability to get supported features.
> + *
> + * @info: the nesting info provided by IOMMU driver.
> + */
> +#define VFIO_IOMMU_TYPE1_INFO_CAP_NESTING 3
> +
> +struct vfio_iommu_type1_info_cap_nesting {
> + struct vfio_info_cap_header header;
> + struct iommu_nesting_info info;
> +};
> +
> #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
>
> /**