On Thu, Jun 11, 2020 at 05:15:33AM -0700, Liu Yi L wrote: > 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> > --- > 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 | 64 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 64 insertions(+) > > diff --git a/Documentation/driver-api/vfio.rst b/Documentation/driver-api/vfio.rst > index f1a4d3c..06224bd 100644 > --- a/Documentation/driver-api/vfio.rst > +++ b/Documentation/driver-api/vfio.rst > @@ -239,6 +239,70 @@ 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 configuration structures and page table s/as long configuration/as long as configuration/ > +format are compatible between the virtual IOMMU and the physical IOMMU. s/format/formats/ > + > +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 > +available 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); It is not clear how the userspace application determines whether PASIDs must be allocated from the host via VFIO_IOMMU_PASID_REQUEST or if the guest itself can allocate PASIDs. The text mentions VFIO_IOMMU_GET_INFO but what exactly should the userspace application check?
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