[v3,13/14] vfio: Document dual stage control

Commit Message

Yi Liu June 24, 2020, 8:55 a.m. UTC

From: Eric Auger <[e-mail]>

The VFIO API was enhanced to support nested stage control: a bunch of
new iotcls and usage guideline.

Let's document the process to follow to set up nested mode.

Cc: Kevin Tian <[e-mail]>
CC: Jacob Pan <[e-mail]>
Cc: Alex Williamson <[e-mail]>
Cc: Eric Auger <[e-mail]>
Cc: Jean-Philippe Brucker <[e-mail]>
Cc: Joerg Roedel <[e-mail]>
Cc: Lu Baolu <[e-mail]>
Signed-off-by: Eric Auger <[e-mail]>
Signed-off-by: Liu Yi L <[e-mail]>
---
v2 -> v3:
*) address comments from Stefan Hajnoczi

v1 -> v2:
*) new in v2, compared with Eric's original version, pasid table bind
   and fault reporting is removed as this series doesn't cover them.
   Original version from Eric.
   https://lkml.org/lkml/2020/3/20/700

 Documentation/driver-api/vfio.rst | 67 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

Comments

Stefan Hajnoczi June 29, 2020, 9:21 a.m. UTC | #1

On Wed, Jun 24, 2020 at 01:55:26AM -0700, Liu Yi L wrote:
> +Details can be found in Documentation/userspace-api/iommu.rst. For Intel
> +VT-d, each stage 1 page table is bound to host by:
> +
> +    nesting_op->flags = VFIO_IOMMU_NESTING_OP_BIND_PGTBL;
> +    memcpy(&nesting_op->data, &bind_data, sizeof(bind_data));
> +    ioctl(container->fd, VFIO_IOMMU_NESTING_OP, nesting_op);
> +
> +As mentioned above, guest OS may use stage 1 for GIOVA->GPA or GVA->GPA.
> +GVA->GPA page tables are available when PASID (Process Address Space ID)
> +is exposed to guest. e.g. guest with PASID-capable devices assigned. For
> +such page table binding, the bind_data should include PASID info, which
> +is allocated by guest itself or by host. This depends on hardware vendor
> +e.g. Intel VT-d requires to allocate PASID from host. This requirement is
> +defined by the Virtual Command Support in VT-d 3.0 spec, guest software
> +running on VT-d should allocate PASID from host kernel. To allocate PASID
> +from host, user space should +check the IOMMU_NESTING_FEAT_SYSWIDE_PASID

s/+check/check/g

Reviewed-by: Stefan Hajnoczi <[e-mail]>

Yi Liu June 29, 2020, 9:24 a.m. UTC | #2

> From: Stefan Hajnoczi <[e-mail]>
> Sent: Monday, June 29, 2020 5:22 PM
> 
> On Wed, Jun 24, 2020 at 01:55:26AM -0700, Liu Yi L wrote:
> > +Details can be found in Documentation/userspace-api/iommu.rst. For
> > +Intel VT-d, each stage 1 page table is bound to host by:
> > +
> > +    nesting_op->flags = VFIO_IOMMU_NESTING_OP_BIND_PGTBL;
> > +    memcpy(&nesting_op->data, &bind_data, sizeof(bind_data));
> > +    ioctl(container->fd, VFIO_IOMMU_NESTING_OP, nesting_op);
> > +
> > +As mentioned above, guest OS may use stage 1 for GIOVA->GPA or GVA->GPA.
> > +GVA->GPA page tables are available when PASID (Process Address Space
> > +GVA->ID)
> > +is exposed to guest. e.g. guest with PASID-capable devices assigned.
> > +For such page table binding, the bind_data should include PASID info,
> > +which is allocated by guest itself or by host. This depends on
> > +hardware vendor e.g. Intel VT-d requires to allocate PASID from host.
> > +This requirement is defined by the Virtual Command Support in VT-d
> > +3.0 spec, guest software running on VT-d should allocate PASID from
> > +host kernel. To allocate PASID from host, user space should +check
> > +the IOMMU_NESTING_FEAT_SYSWIDE_PASID
> 
> s/+check/check/g

got it.

> Reviewed-by: Stefan Hajnoczi <[e-mail]>

thanks :-)

Regards,
Yi Liu

Patch

diff --git a/Documentation/driver-api/vfio.rst b/Documentation/driver-api/vfio.rst
index f1a4d3c..639890f 100644
--- a/Documentation/driver-api/vfio.rst
+++ b/Documentation/driver-api/vfio.rst
@@ -239,6 +239,73 @@  group and can access them as follows::
 	/* Gratuitous device reset and go... */
 	ioctl(device, VFIO_DEVICE_RESET);
 
+IOMMU Dual Stage Control
+------------------------
+
+Some IOMMUs support 2 stages/levels of translation. Stage corresponds to
+the ARM terminology while level corresponds to Intel's VTD terminology.
+In the following text we use either without distinction.
+
+This is useful when the guest is exposed with a virtual IOMMU and some
+devices are assigned to the guest through VFIO. Then the guest OS can use
+stage 1 (GIOVA -> GPA or GVA->GPA), while the hypervisor uses stage 2 for
+VM isolation (GPA -> HPA).
+
+Under dual stage translation, the guest gets ownership of the stage 1 page
+tables and also owns stage 1 configuration structures. The hypervisor owns
+the root configuration structure (for security reason), including stage 2
+configuration. This works as long as configuration structures and page table
+formats are compatible between the virtual IOMMU and the physical IOMMU.
+
+Assuming the HW supports it, this nested mode is selected by choosing the
+VFIO_TYPE1_NESTING_IOMMU type through:
+
+    ioctl(container, VFIO_SET_IOMMU, VFIO_TYPE1_NESTING_IOMMU);
+
+This forces the hypervisor to use the stage 2, leaving stage 1 available
+for guest usage. The guest stage 1 format depends on IOMMU vendor, and
+it is the same with the nesting configuration method. User space should
+check the format and configuration method after setting nesting type by
+using:
+
+    ioctl(container->fd, VFIO_IOMMU_GET_INFO, &nesting_info);
+
+Details can be found in Documentation/userspace-api/iommu.rst. For Intel
+VT-d, each stage 1 page table is bound to host by:
+
+    nesting_op->flags = VFIO_IOMMU_NESTING_OP_BIND_PGTBL;
+    memcpy(&nesting_op->data, &bind_data, sizeof(bind_data));
+    ioctl(container->fd, VFIO_IOMMU_NESTING_OP, nesting_op);
+
+As mentioned above, guest OS may use stage 1 for GIOVA->GPA or GVA->GPA.
+GVA->GPA page tables are available when PASID (Process Address Space ID)
+is exposed to guest. e.g. guest with PASID-capable devices assigned. For
+such page table binding, the bind_data should include PASID info, which
+is allocated by guest itself or by host. This depends on hardware vendor
+e.g. Intel VT-d requires to allocate PASID from host. This requirement is
+defined by the Virtual Command Support in VT-d 3.0 spec, guest software
+running on VT-d should allocate PASID from host kernel. To allocate PASID
+from host, user space should +check the IOMMU_NESTING_FEAT_SYSWIDE_PASID
+bit of the nesting info reported from host kernel. VFIO reports the nesting
+info by VFIO_IOMMU_GET_INFO. User space could allocate PASID from host by:
+
+    req.flags = VFIO_IOMMU_ALLOC_PASID;
+    ioctl(container, VFIO_IOMMU_PASID_REQUEST, &req);
+
+With first stage/level page table bound to host, it allows to combine the
+guest stage 1 translation along with the hypervisor stage 2 translation to
+get final address.
+
+When the guest invalidates stage 1 related caches, invalidations must be
+forwarded to the host through
+
+    nesting_op->flags = VFIO_IOMMU_NESTING_OP_CACHE_INVLD;
+    memcpy(&nesting_op->data, &inv_data, sizeof(inv_data));
+    ioctl(container->fd, VFIO_IOMMU_NESTING_OP, nesting_op);
+
+Those invalidations can happen at various granularity levels, page, context,
+...
+
 VFIO User API
 -------------------------------------------------------------------------------