On 12/24/19 3:44 PM, Lu Baolu wrote:
Intel VT-d in scalable mode supports two types of page tables
for DMA translation: the first level page table and the second
level page table. The first level page table uses the same
format as the CPU page table, while the second level page table
keeps compatible with previous formats. The software is able
to choose any one of them for DMA remapping according to the use
case.
This patchset aims to move IOVA (I/O Virtual Address) translation
to 1st-level page table in scalable mode. This will simplify vIOMMU
(IOMMU simulated by VM hypervisor) design by using the two-stage
translation, a.k.a. nested mode translation.
As Intel VT-d architecture offers caching mode, guest IOVA (GIOVA)
support is currently implemented in a shadow page manner. The device
simulation software, like QEMU, has to figure out GIOVA->GPA mappings
and write them to a shadowed page table, which will be used by the
physical IOMMU. Each time when mappings are created or destroyed in
vIOMMU, the simulation software has to intervene. Hence, the changes
on GIOVA->GPA could be shadowed to host.
.-----------.
| vIOMMU |
|-----------| .--------------------.
| |IOTLB flush trap | QEMU |
.-----------. (map/unmap) |--------------------|
|GIOVA->GPA |---------------->| .------------. |
'-----------' | | GIOVA->HPA | |
| | | '------------' |
'-----------' | |
| |
'--------------------'
|
<------------------------------------
|
v VFIO/IOMMU API
.-----------.
| pIOMMU |
|-----------|
| |
.-----------.
|GIOVA->HPA |
'-----------'
| |
'-----------'
In VT-d 3.0, scalable mode is introduced, which offers two-level
translation page tables and nested translation mode. Regards to
GIOVA support, it can be simplified by 1) moving the GIOVA support
over 1st-level page table to store GIOVA->GPA mapping in vIOMMU,
2) binding vIOMMU 1st level page table to the pIOMMU, 3) using pIOMMU
second level for GPA->HPA translation, and 4) enable nested (a.k.a.
dual-stage) translation in host. Compared with current shadow GIOVA
support, the new approach makes the vIOMMU design simpler and more
efficient as we only need to flush the pIOMMU IOTLB and possible
device-IOTLB when an IOVA mapping in vIOMMU is torn down.
.-----------.
| vIOMMU |
|-----------| .-----------.
| |IOTLB flush trap | QEMU |
.-----------. (unmap) |-----------|
|GIOVA->GPA |---------------->| |
'-----------' '-----------'
| | |
'-----------' |
<------------------------------
| VFIO/IOMMU
| cache invalidation and
| guest gpd bind interfaces
v
.-----------.
| pIOMMU |
|-----------|
.-----------.
|GIOVA->GPA |<---First level
'-----------'
| GPA->HPA |<---Scond level
'-----------'
'-----------'
This patch applies the first level page table for IOVA translation
unless the DOMAIN_ATTR_NESTING domain attribution has been set.
Setting of this attribution means the second level will be used to
map gPA (guest physical address) to hPA (host physical address), and
the mappings between gVA (guest virtual address) and gPA will be
maintained by the guest with the page table address binding to host's
first level.
Based-on-idea-by: Ashok Raj<ashok.raj@xxxxxxxxx>
Based-on-idea-by: Kevin Tian<kevin.tian@xxxxxxxxx>
Based-on-idea-by: Liu Yi L<yi.l.liu@xxxxxxxxx>
Based-on-idea-by: Jacob Pan<jacob.jun.pan@xxxxxxxxxxxxxxx>
Based-on-idea-by: Sanjay Kumar<sanjay.k.kumar@xxxxxxxxx>
Based-on-idea-by: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
Queued all patches for v5.6.
Thanks,
-baolu
