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

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Jacob,

On 9/24/19 3:27 AM, Jacob Pan wrote:
> Hi Baolu,
> 
> On Mon, 23 Sep 2019 20:24:50 +0800
> Lu Baolu <baolu.lu@linux.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.

There should be no page fault. The pages should have been pinned.

> 
> 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?

Yes. There isn't such use case as far as I can see.

Best regards,
Baolu

>>       .-----------.
>>       |  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@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: Lu Baolu <baolu.lu@linux.intel.com>
>> Based-on-idea-by: Sanjay Kumar <sanjay.k.kumar@intel.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]
> 
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu