Re: [Qemu-devel] [RFC v2 0/3] intel_iommu: support scalable mode

[Peter Xu]

On Thu, Feb 28, 2019 at 09:47:54PM +0800, Yi Sun wrote:
> Intel vt-d rev3.0 [1] introduces a new translation mode called
> 'scalable mode', which enables PASID-granular translations for
> first level, second level, nested and pass-through modes. The
> vt-d scalable mode is the key ingredient to enable Scalable I/O
> Virtualization (Scalable IOV) [2] [3], which allows sharing a
> device in minimal possible granularity (ADI - Assignable Device
> Interface). As a result, previous Extended Context (ECS) mode
> is deprecated (no production ever implements ECS).
> 
> This patch set emulates a minimal capability set of VT-d scalable
> mode, equivalent to what is available in VT-d legacy mode today:
>     1. Scalable mode root entry, context entry and PASID table
>     2. Seconds level translation under scalable mode
>     3. Queued invalidation (with 256 bits descriptor)
>     4. Pass-through mode
> 
> Corresponding intel-iommu driver support will be included in
> kernel 5.0:
>     https://www.spinics.net/lists/kernel/msg2985279.html
> 
> We will add emulation of full scalable mode capability along with
> guest iommu driver progress later, e.g.:
>     1. First level translation
>     2. Nested translation
>     3. Per-PASID invalidation descriptors
>     4. Page request services for handling recoverable faults
> 
> To verify the patches, below cases were tested according to Peter Xu's
> suggestions.
>     
> +---------+----------------------------------------------------------------+----------------------------------------------------------------+
>     |         |                      w/ Device Passthr                        
>  |                     w/o Device Passthr                         |
>     |         
> +-------------------------------+--------------------------------+-------------------------------+--------------------------------+
>     |         | virtio-net-pci, vhost=on      | virtio-net-pci, vhost=off     
>  | virtio-net-pci, vhost=on      | virtio-net-pci, vhost=off      |
>     |         
> +-------------------------------+--------------------------------+-------------------------------+--------------------------------+
>     |         | netperf | kernel bld | data cp| netperf | kernel bld | data 
> cp | netperf | kernel bld | data cp| netperf | kernel bld | data cp |
>     
> +---------+-------------------------------+--------------------------------+-------------------------------+--------------------------------+
>     | Legacy  | Pass    | Pass       | Pass   | Pass    | Pass       | Pass   
>  | Pass    | Pass       | Pass   | Pass    | Pass       | Pass    |
>     
> +---------+-------------------------------+--------------------------------+-------------------------------+--------------------------------+
>     | Scalable| Pass    | Pass       | Pass   | Pass    | Pass       | Pass   
>  | Pass    | Pass       | Pass   | Pass    | Pass       | Pass    |
>     
> +---------+-------------------------------+--------------------------------+-------------------------------+--------------------------------+

Hi, Yi,

Thanks very much for the thorough test matrix!

The last thing I'd like to confirm is have you tested device
assignment with v2?  And note that when you test with virtio devices
you should not need caching-mode=on (but caching-mode=on should not
break anyone though).

I've still got some comments here and there but it looks very good at
least to me overall.

Thanks,

-- 
Peter Xu