linux-kernel - Re: [PATCH v2 00/15] vfio: expose virtual Shared Virtual Addressing to VMs

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Message-ID: <20200615100214.GC1491454@stefanha-x1.localdomain>
Date:   Mon, 15 Jun 2020 11:02:14 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Liu Yi L <yi.l.liu@...el.com>
Cc:     alex.williamson@...hat.com, eric.auger@...hat.com,
        baolu.lu@...ux.intel.com, joro@...tes.org, kevin.tian@...el.com,
        jacob.jun.pan@...ux.intel.com, ashok.raj@...el.com,
        jun.j.tian@...el.com, yi.y.sun@...el.com, jean-philippe@...aro.org,
        peterx@...hat.com, hao.wu@...el.com,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/15] vfio: expose virtual Shared Virtual Addressing
 to VMs

On Thu, Jun 11, 2020 at 05:15:19AM -0700, Liu Yi L wrote:
> Shared Virtual Addressing (SVA), a.k.a, Shared Virtual Memory (SVM) on
> Intel platforms allows address space sharing between device DMA and
> applications. SVA can reduce programming complexity and enhance security.
> 
> This VFIO series is intended to expose SVA usage to VMs. i.e. Sharing
> guest application address space with passthru devices. This is called
> vSVA in this series. The whole vSVA enabling requires QEMU/VFIO/IOMMU
> changes. For IOMMU and QEMU changes, they are in separate series (listed
> in the "Related series").
> 
> The high-level architecture for SVA virtualization is as below, the key
> design of vSVA support is to utilize the dual-stage IOMMU translation (
> also known as IOMMU nesting translation) capability in host IOMMU.
> 
> 
>     .-------------.  .---------------------------.
>     |   vIOMMU    |  | Guest process CR3, FL only|
>     |             |  '---------------------------'
>     .----------------/
>     | PASID Entry |--- PASID cache flush -
>     '-------------'                       |
>     |             |                       V
>     |             |                CR3 in GPA
>     '-------------'
> Guest
> ------| Shadow |--------------------------|--------
>       v        v                          v
> Host
>     .-------------.  .----------------------.
>     |   pIOMMU    |  | Bind FL for GVA-GPA  |
>     |             |  '----------------------'
>     .----------------/  |
>     | PASID Entry |     V (Nested xlate)
>     '----------------\.------------------------------.
>     |             |   |SL for GPA-HPA, default domain|
>     |             |   '------------------------------'
>     '-------------'
> Where:
>  - FL = First level/stage one page tables
>  - SL = Second level/stage two page tables

Hi,
Looks like an interesting feature!

To check I understand this feature: can applications now pass virtual
addresses to devices instead of translating to IOVAs?

If yes, can guest applications restrict the vSVA address space so the
device only has access to certain regions?

On one hand replacing IOVA translation with virtual addresses simplifies
the application programming model, but does it give up isolation if the
device can now access all application memory?

Thanks,
Stefan

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