From: Eric Auger <eric.auger@xxxxxxxxxx> 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 <kevin.tian@xxxxxxxxx> CC: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx> Cc: Eric Auger <eric.auger@xxxxxxxxxx> Cc: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> Cc: Joerg Roedel <joro@xxxxxxxxxx> Cc: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx> Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx> --- 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(+) 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 ------------------------------------------------------------------------------- -- 2.7.4
