> From: Lu Baolu [mailto:baolu.lu@xxxxxxxxxxxxxxx] > Sent: Thursday, January 2, 2020 7:38 AM > To: Joerg Roedel <joro@xxxxxxxxxx>; David Woodhouse <dwmw2@xxxxxxxxxxxxx>; > Alex Williamson <alex.williamson@xxxxxxxxxx> > Subject: Re: [PATCH v5 0/9] Use 1st-level for IOVA translation > > 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. Reviewed-by: Liu Yi L <yi.l.liu@xxxxxxxxx> Aha, looks like I forgot to give my Reviewed-by after offline review.. Yeah, this patchset looks good to me. Regards, Yi Liu > Thanks, > -baolu
