Re: [PATCH v5 0/9] Use 1st-level for IOVA translation

Lu Baolu
2020-01-02T02:33:21Z

Hi Yi,

On 1/2/20 10:31 AM, Liu, Yi L wrote:
>> From: Lu Baolu [mailto:baolu.lu@linux.intel.com]
>> Sent: Thursday, January 2, 2020 7:38 AM
>> To: Joerg Roedel <joro@8bytes.org>; David Woodhouse <dwmw2@infradead.org>;
>> Alex Williamson <alex.williamson@redhat.com>
>> 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@intel.com>
>>> Based-on-idea-by: Kevin Tian<kevin.tian@intel.com>
>>> Based-on-idea-by: Liu Yi L<yi.l.liu@intel.com>
>>> Based-on-idea-by: Jacob Pan<jacob.jun.pan@linux.intel.com>
>>> Based-on-idea-by: Sanjay Kumar<sanjay.k.kumar@intel.com>
>>> Based-on-idea-by: Lu Baolu<baolu.lu@linux.intel.com>
>>
>> Queued all patches for v5.6.
>
> Reviewed-by: Liu Yi L <yi.l.liu@intel.com>
>
> Aha, looks like I forgot to give my Reviewed-by after offline review..
> Yeah, this patchset looks good to me.

Thank you, Yi. Very appreciated for your time.

Best regards,
-baolu