Re: [RFC v2 3/3] vfio/type1: bind guest pasid (guest page tables) to host

Alex Williamson
2019-11-07T23:20:56Z

On Thu, 24 Oct 2019 08:26:23 -0400
Liu Yi L <yi.l.liu@intel.com> wrote:

> This patch adds vfio support to bind guest translation structure
> to host iommu. VFIO exposes iommu programming capability to user-
> space. Guest is a user-space application in host under KVM solution.
> For SVA usage in Virtual Machine, guest owns GVA->GPA translation
> structure. And this part should be passdown to host to enable nested
> translation (or say two stage translation). This patch reuses the
> VFIO_IOMMU_BIND proposal from Jean-Philippe Brucker, and adds new
> bind type for binding guest owned translation structure to host.
>
> *) Add two new ioctls for VFIO containers.
>
> - VFIO_IOMMU_BIND: for bind request from userspace, it could be
> bind a process to a pasid or bind a guest pasid
> to a device, this is indicated by type
> - VFIO_IOMMU_UNBIND: for unbind request from userspace, it could be
> unbind a process to a pasid or unbind a guest pasid
> to a device, also indicated by type
> - Bind type:
> VFIO_IOMMU_BIND_PROCESS: user-space request to bind a process
> to a device
> VFIO_IOMMU_BIND_GUEST_PASID: bind guest owned translation
> structure to host iommu. e.g. guest page table
>
> *) Code logic in vfio_iommu_type1_ioctl() to handle VFIO_IOMMU_BIND/UNBIND
>
> Cc: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 136 ++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/vfio.h | 44 +++++++++++++
> 2 files changed, 180 insertions(+)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 3d73a7d..1a27e25 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -2325,6 +2325,104 @@ static int vfio_iommu_type1_pasid_free(struct vfio_iommu *iommu,
> return ret;
> }
>
> +static int vfio_bind_gpasid_fn(struct device *dev, void *data)
> +{
> + struct domain_capsule *dc = (struct domain_capsule *)data;
> + struct iommu_gpasid_bind_data *ustruct =
> + (struct iommu_gpasid_bind_data *) dc->data;
> +
> + return iommu_sva_bind_gpasid(dc->domain, dev, ustruct);
> +}
> +
> +static int vfio_unbind_gpasid_fn(struct device *dev, void *data)
> +{
> + struct domain_capsule *dc = (struct domain_capsule *)data;
> + struct iommu_gpasid_bind_data *ustruct =
> + (struct iommu_gpasid_bind_data *) dc->data;
> +
> + return iommu_sva_unbind_gpasid(dc->domain, dev,
> + ustruct->hpasid);
> +}
> +
> +/*
> + * unbind specific gpasid, caller of this function requires hold
> + * vfio_iommu->lock
> + */
> +static long vfio_iommu_type1_do_guest_unbind(struct vfio_iommu *iommu,
> + struct iommu_gpasid_bind_data *gbind_data)
> +{
> + return vfio_iommu_lookup_dev(iommu, vfio_unbind_gpasid_fn, gbind_data);
> +}
> +
> +static long vfio_iommu_type1_bind_gpasid(struct vfio_iommu *iommu,
> + void __user *arg,
> + struct vfio_iommu_type1_bind *bind)
> +{
> + struct iommu_gpasid_bind_data gbind_data;
> + unsigned long minsz;
> + int ret = 0;
> +
> + minsz = sizeof(*bind) + sizeof(gbind_data);
> + if (bind->argsz < minsz)
> + return -EINVAL;
> +
> + if (copy_from_user(&gbind_data, arg, sizeof(gbind_data)))
> + return -EFAULT;
> +
> + mutex_lock(&iommu->lock);
> + if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) {
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> +
> + ret = vfio_iommu_lookup_dev(iommu, vfio_bind_gpasid_fn, &gbind_data);
> + /*
> + * If bind failed, it may not be a total failure. Some devices within
> + * the iommu group may have bind successfully. Although we don't enable
> + * pasid capability for non-singletion iommu groups, a unbind operation
> + * would be helpful to ensure no partial binding for an iommu group.
> + */
> + if (ret)
> + /*
> + * Undo all binds that already succeeded, no need to check the
> + * return value here since some device within the group has no
> + * successful bind when coming to this place switch.
> + */
> + vfio_iommu_type1_do_guest_unbind(iommu, &gbind_data);
> +
> +out_unlock:
> + mutex_unlock(&iommu->lock);
> + return ret;
> +}
> +
> +static long vfio_iommu_type1_unbind_gpasid(struct vfio_iommu *iommu,
> + void __user *arg,
> + struct vfio_iommu_type1_bind *bind)
> +{
> + struct iommu_gpasid_bind_data gbind_data;
> + unsigned long minsz;
> + int ret = 0;
> +
> + minsz = sizeof(*bind) + sizeof(gbind_data);
> + if (bind->argsz < minsz)
> + return -EINVAL;

But gbind_data can change size if new vendor specific data is added to
the union, so kernel updates break existing userspace. Fail.

> +
> + if (copy_from_user(&gbind_data, arg, sizeof(gbind_data)))
> + return -EFAULT;
> +
> + mutex_lock(&iommu->lock);
> + if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) {
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> +
> + ret = vfio_iommu_type1_do_guest_unbind(iommu, &gbind_data);
> +
> +out_unlock:
> + mutex_unlock(&iommu->lock);
> + return ret;
> +}
> +
> static long vfio_iommu_type1_ioctl(void *iommu_data,
> unsigned int cmd, unsigned long arg)
> {
> @@ -2484,6 +2582,44 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
> default:
> return -EINVAL;
> }
> +
> + } else if (cmd == VFIO_IOMMU_BIND) {
> + struct vfio_iommu_type1_bind bind;
> +
> + minsz = offsetofend(struct vfio_iommu_type1_bind, bind_type);
> +
> + if (copy_from_user(&bind, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (bind.argsz < minsz)
> + return -EINVAL;
> +
> + switch (bind.bind_type) {
> + case VFIO_IOMMU_BIND_GUEST_PASID:
> + return vfio_iommu_type1_bind_gpasid(iommu,
> + (void __user *)(arg + minsz), &bind);

Why are we defining BIND_PROCESS if it's not supported? How does the
user learn it's not supported?

> + default:
> + return -EINVAL;
> + }
> +
> + } else if (cmd == VFIO_IOMMU_UNBIND) {
> + struct vfio_iommu_type1_bind bind;
> +
> + minsz = offsetofend(struct vfio_iommu_type1_bind, bind_type);
> +
> + if (copy_from_user(&bind, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (bind.argsz < minsz)
> + return -EINVAL;
> +
> + switch (bind.bind_type) {
> + case VFIO_IOMMU_BIND_GUEST_PASID:
> + return vfio_iommu_type1_unbind_gpasid(iommu,
> + (void __user *)(arg + minsz), &bind);
> + default:
> + return -EINVAL;
> + }
> }
>
> return -ENOTTY;
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 04de290..78e8c64 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -832,6 +832,50 @@ struct vfio_iommu_type1_pasid_request {
> */
> #define VFIO_IOMMU_PASID_REQUEST _IO(VFIO_TYPE, VFIO_BASE + 27)
>
> +enum vfio_iommu_bind_type {
> + VFIO_IOMMU_BIND_PROCESS,
> + VFIO_IOMMU_BIND_GUEST_PASID,
> +};
> +
> +/*
> + * Supported types:
> + * - VFIO_IOMMU_BIND_GUEST_PASID: bind guest pasid, which invoked
> + * by guest, it takes iommu_gpasid_bind_data in data.
> + */
> +struct vfio_iommu_type1_bind {
> + __u32 argsz;
> + enum vfio_iommu_bind_type bind_type;
> + __u8 data[];
> +};

I don't think enum defines a compiler invariant data size. We can't
use it for a kernel/user interface. Also why no flags field as is
essentially standard for every vfio ioctl? Couldn't we specify
process/guest-pasid with flags? For that matter couldn't we specify
bind/unbind using a single ioctl? I think that would be more
consistent with the pasid alloc/free ioctl in the previous patch.

Why are we appending opaque data to the end of the structure when
clearly we expect a struct iommu_gpasid_bind_data? That bind data
structure expects a format (ex. IOMMU_PASID_FORMAT_INTEL_VTD). How does
a user determine what formats are accepted from within the vfio API (or
even outside of the vfio API)?

> +
> +/*
> + * VFIO_IOMMU_BIND - _IOWR(VFIO_TYPE, VFIO_BASE + 28, struct vfio_iommu_bind)
^
The semantics appear to just be _IOW, nothing is written back to the
userspace buffer on return.

> + *
> + * Manage address spaces of devices in this container. Initially a TYPE1
> + * container can only have one address space, managed with
> + * VFIO_IOMMU_MAP/UNMAP_DMA.
> + *
> + * An IOMMU of type VFIO_TYPE1_NESTING_IOMMU can be managed by both MAP/UNMAP
> + * and BIND ioctls at the same time. MAP/UNMAP acts on the stage-2 (host) page
> + * tables, and BIND manages the stage-1 (guest) page tables. Other types of
> + * IOMMU may allow MAP/UNMAP and BIND to coexist, where MAP/UNMAP controls
> + * non-PASID traffic and BIND controls PASID traffic. But this depends on the
> + * underlying IOMMU architecture and isn't guaranteed.
> + *
> + * Availability of this feature depends on the device, its bus, the underlying
> + * IOMMU and the CPU architecture.

And the user discovers this is available by...? There's no probe here,
are they left only to setup a VM to the point of trying to use this
before they fail the ioctl? Could VFIO_IOMMU_GET_INFO fill this gap?
Thanks,

Alex

> + *
> + * returns: 0 on success, -errno on failure.
> + */
> +#define VFIO_IOMMU_BIND _IO(VFIO_TYPE, VFIO_BASE + 28)
> +
> +/*
> + * VFIO_IOMMU_UNBIND - _IOWR(VFIO_TYPE, VFIO_BASE + 29, struct vfio_iommu_bind)
> + *
> + * Undo what was done by the corresponding VFIO_IOMMU_BIND ioctl.
> + */
> +#define VFIO_IOMMU_UNBIND _IO(VFIO_TYPE, VFIO_BASE + 29)
> +
> /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
>
> /*