linux-kernel - Re: [RFC PATCH 0/4] Use 1st-level for DMA remapping in guest

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Message-ID: <20190923122715.53de79d0@jacob-builder>
Date:   Mon, 23 Sep 2019 12:27:15 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        ashok.raj@...el.com, sanjay.k.kumar@...el.com,
        kevin.tian@...el.com, yi.l.liu@...el.com, yi.y.sun@...el.com,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC PATCH 0/4] Use 1st-level for DMA remapping in guest

Hi Baolu,

On Mon, 23 Sep 2019 20:24:50 +0800
Lu Baolu <baolu.lu@...ux.intel.com> wrote:

> This patchset aims to move IOVA (I/O Virtual Address) translation
> to 1st-level page table under scalable mode. The major purpose of
> this effort is to make guest IOVA support more efficient.
> 
> As Intel VT-d architecture offers caching-mode, guest IOVA (GIOVA)
> support is now implemented in a shadow page manner. The device
> simulation software, like QEMU, has to figure out GIOVA->GPA mapping
> and writes to a shadowed page table, which will be used by pIOMMU.
> Each time when mappings are created or destroyed in vIOMMU, the
> simulation software will intervene. The change on GIOVA->GPA will be
> shadowed to host, and the pIOMMU will be updated via VFIO/IOMMU
> interfaces.
> 
> 
>      .-----------.
>      |  vIOMMU   |
>      |-----------|                 .--------------------.
>      |           |IOTLB flush trap |        QEMU        |
>      .-----------. (map/unmap)     |--------------------|
>      | GVA->GPA  |---------------->|      .----------.  |
>      '-----------'                 |      | GPA->HPA |  |
>      |           |                 |      '----------'  |
>      '-----------'                 |                    |
>                                    |                    |
>                                    '--------------------'
>                                                 |
>             <------------------------------------
>             |
>             v VFIO/IOMMU API
>       .-----------.
>       |  pIOMMU   |
>       |-----------|
>       |           |
>       .-----------.
>       | GVA->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 is more secure and software is simplified
> 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)      |-----------|
>      | GVA->GPA  |---------------->|           |
>      '-----------'                 '-----------'
>      |           |                       |
>      '-----------'                       |
>            <------------------------------
>            |      VFIO/IOMMU          
>            |  cache invalidation and  
>            | guest gpd bind interfaces
>            v
For vSVA, the guest PGD bind interface will mark the PASID as guest
PASID and will inject page request into the guest. In FL gIOVA case, I
guess we are assuming there is no page fault for GIOVA. I will need to
add a flag in the gpgd bind such that any PRS will be auto responded
with invalid.

Also, native use of IOVA FL map is not to be supported? i.e. IOMMU API
and DMA API for native usage will continue to be SL only?
>      .-----------.
>      |  pIOMMU   |
>      |-----------|
>      .-----------.
>      | GVA->GPA  |<---First level
>      '-----------'
>      | GPA->HPA  |<---Scond level
>      '-----------'
>      '-----------'
> 
> This patch series only aims to achieve the first goal, a.k.a using
> first level translation for IOVA mappings in vIOMMU. I am sending
> it out for your comments. Any comments, suggestions and concerns are
> welcomed.
> 


> Based-on-idea-by: Ashok Raj <ashok.raj@...el.com>
> Based-on-idea-by: Kevin Tian <kevin.tian@...el.com>
> Based-on-idea-by: Liu Yi L <yi.l.liu@...el.com>
> Based-on-idea-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Based-on-idea-by: Sanjay Kumar <sanjay.k.kumar@...el.com>
> 
> Lu Baolu (4):
>   iommu/vt-d: Move domain_flush_cache helper into header
>   iommu/vt-d: Add first level page table interfaces
>   iommu/vt-d: Map/unmap domain with mmmap/mmunmap
>   iommu/vt-d: Identify domains using first level page table
> 
>  drivers/iommu/Makefile             |   2 +-
>  drivers/iommu/intel-iommu.c        | 142 ++++++++++--
>  drivers/iommu/intel-pgtable.c      | 342
> +++++++++++++++++++++++++++++ include/linux/intel-iommu.h        |
> 31 ++- include/trace/events/intel_iommu.h |  60 +++++
>  5 files changed, 553 insertions(+), 24 deletions(-)
>  create mode 100644 drivers/iommu/intel-pgtable.c
> 

[Jacob Pan]