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

From: Lu Baolu <baolu.lu@linux.intel.com>
To: Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Alex Williamson <alex.williamson@redhat.com>
Cc: baolu.lu@linux.intel.com, ashok.raj@intel.com,
	sanjay.k.kumar@intel.com, jacob.jun.pan@linux.intel.com,
	kevin.tian@intel.com, yi.l.liu@intel.com, yi.y.sun@intel.com,
	Peter Xu <peterx@redhat.com>,
	iommu@lists.linux-foundation.org, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 0/9] Use 1st-level for IOVA translation
Date: Thu, 2 Jan 2020 07:38:23 +0800	[thread overview]
Message-ID: <8b40dd00-3bec-1fd9-9ba7-0db9fd727e52@linux.intel.com> (raw)
In-Reply-To: <20191224074502.5545-1-baolu.lu@linux.intel.com>

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.

Thanks,
-baolu