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

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Date:   Mon, 23 Sep 2019 13:25:52 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.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,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [RFC PATCH 0/4] Use 1st-level for DMA remapping in guest

Hi Jacob

On Mon, Sep 23, 2019 at 12:27:15PM -0700, Jacob Pan wrote:
> > 
> > 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.

Is there real need to enforce this? I'm not sure if there is any
limitation in the spec, and if so, can the guest check that instead?

Also i believe the idea is to overcommit PASID#0 such uses. Thought
we had a capability to expose this to the vIOMMU as well. Not sure if this
is already documented, if not should be up in the next rev.


> 
> 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

s/Scond/Second

> >      '-----------'
> >      '-----------'
> > 
> > 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]