On Fri, Aug 04, 2017 at 07:19:25PM +0100, Jean-Philippe Brucker wrote:
> This is the continuation of my proposal for virtio-iommu, the para-
> virtualized IOMMU. Here is a summary of the changes since last time [1]:
>
> * The virtio-iommu document now resembles an actual specification. It is
> split into a formal description of the virtio device, and implementation
> notes. Please find sources and binaries at [2].
>
> * Added a probe request to describe to the guest different properties that
> do not fit in firmware or in the virtio config space. This is a
> necessary stepping stone for extending the virtio-iommu.
>
> * There is a working Qemu prototype [3], thanks to Eric Auger and Bharat
> Bhushan.
Hi, Brucker
I read the related spec for virtio IOMMU,
I am wondering if we support both the virtual and physical devices in
the guest to use the virtio IOMMU, how can we config the related address
translation for the different type of devices.
e.g.
1. for Virtio devs(e.g. virtio-net), we can change the memmap table used
by the vhost device.
2. for physical devices we can directly config the IOMMU/SMMU on the
host.
So do you know are there any RFCs for the back-end implementation for the
virtio-IOMMU
thanks
Adam
>
> You can find the Linux driver and kvmtool device at [4] and [5]. I
> plan to rework driver and kvmtool device slightly before sending the
> patches.
>
> To understand the virtio-iommu, I advise to first read introduction and
> motivation, then skim through implementation notes and finally look at the
> device specification.
>
> I wasn't sure how to organize the review. For those who prefer to comment
> inline, I attached v0.4 of device-operations.tex and topology.tex+MSI.tex
> to this thread. They are the biggest chunks of the document. But LaTeX
> isn't very pleasant to read, so you can simply send a list of comments in
> relation to section numbers and a few words of context, we'll manage.
>
> ---
> Version numbers 0.1-0.4 are arbitrary. I'm hoping they allow to compare
> more easily differences since the RFC (see [6]), but haven't been made
> public so far. This is the first public posting since initial proposal
> [1], and the following describes all changes.
>
> ## v0.1 ##
>
> Content is the same as the RFC, but formatted to LaTeX. 'make' generates
> one PDF and one HTML document.
>
> ## v0.2 ##
>
> Add introductions, improve topology example and firmware description based
> on feedback and a number of useful discussions.
>
> ## v0.3 ##
>
> Add normative sections (MUST, SHOULD, etc). Clarify some things, tighten
> the device and driver behaviour. Unmap semantics are consolidated; they
> are now closer to VFIO Type1 v2 semantics.
>
> ## v0.4 ##
>
> Introduce PROBE requests. They provide per-endpoint information to the
> driver that couldn't be described otherwise.
>
> For the moment, they allow to handle MSIs on x86 virtual platforms (see
> 3.2). To do that we communicate reserved IOVA regions, that will also be
> useful for describing regions that cannot be mapped for a given endpoint,
> for instance addresses that correspond to a PCI bridge window.
>
> Introducing such a large framework for this tiny feature may seem
> overkill, but it is needed for future extensions of the virtio-iommu and I
> believe it really is worth the effort.
>
> ## Future ##
>
> Other extensions are in preparation. I won't detail them here because v0.4
> already is a lot to digest, but in short, building on top of PROBE:
>
> * First, since the IOMMU is paravirtualized, the device can expose some
> properties of the physical topology to the guest, and let it allocate
> resources more efficiently. For example, when the virtio-iommu manages
> both physical and emulated endpoints, with different underlying IOMMUs,
> we now have a way to describe multiple page and block granularities,
> instead of forcing the guest to use the most restricted one for all
> endpoints. This will most likely be in v0.5.
>
> * Then on top of that, a major improvement will describe hardware
> acceleration features available to the guest. There is what I call "Page
> Table Handover" (or simply, from the host POV, "Nested"), the ability
> for the guest to manipulate its own page tables instead of sending
> MAP/UNMAP requests to the host. This, along with IO Page Fault
> reporting, will also permit SVM virtualization on different platforms.
>
> Thanks,
> Jean
>
> [1] http://www.spinics.net/lists/kvm/msg147990.html
> [2] git://linux-arm.org/virtio-iommu.git branch viommu/v0.4
>
> http://www.linux-arm.org/git?p=virtio-iommu.git;a=blob;f=dist/v0.4/virtio-iommu-v0.4.pdf
> I reiterate the disclaimers: don't use this document as a reference,
> it's a draft. It's also not an OASIS document yet. It may be riddled
> with mistakes. As this is a working draft, it is unstable and I do not
> guarantee backward compatibility of future versions.
> [3]
