Re: nested-smmuv3 topic, Sep 2024

[Nicolin Chen <nicolinc@nvidia.com>]

Hi Shameer,

Thanks for the reply!

On Thu, Sep 05, 2024 at 12:55:52PM +0000, Shameerali Kolothum Thodi wrote:
> > The main takeaway from the discussion is to
> > 1) Turn the vSMMU module into a pluggable one, like intel-iommu
> > 2) Move the per-SMMU pxb bus and device auto-assign into libvirt
> >
> > Apart from the multi-vSMMU thing, there's basic nesting series:
> > 0) Keep updating to the latest kernel uAPIs to support nesting
> 
> By this you mean the old HWPT based nested-smmuv3 support?

HWPT + vIOMMU. The for-viommu/virq branches that I shared in my
kernel series have those changes. Invalidations is done via the
vIOMMU infrastructure.

> >
> > I was trying to do all these three, but apparently too ambitious.
> > The kernel side of work is still taking a lot of my bandwidth. So
> > far I had almost-zero progress on task (1) and completely-zero on
> > task (2).
> >
> > <-- Help Needed --->
> > So, I'm wondering if anyone(s) might have some extra bandwidth in
> > the following months helping these two tasks, either of which can
> > be a standalone project I think.
> >
> > For task (0), I think I can keep updating the uAPI part, although
> > it'd need some help for reviews, which I was hoping to occur after
> > Intel sends the QEMU nesting backend patches. Once we know how big
> > the rework is going to be, we may need to borrow some help at that
> > point once again..
> 
> I might have some bandwidth starting October and can take a look at
> task 1 above. I haven't gone through the VIOMMU API model completely
> yet and plan to do that soon.

Thank you! That'd be helpful! The major effort I think is in the
VIRT code also, where "-device nested-smmuv3" must tell the info
to build Device Tree or IORT.

The vIOMMU uAPI is not that complicated. That being said, I am
trying to add some kernel documentation for nested translation,
so hopefully this would be helpful in the near future.

> Also I am planning to attend KVM forum, so if there are anyone interested
> to have  a chat on this, please let me know.

Wish I could make it to that. I think we will need another Oct
thread to get all of us aligned once again.

Regards
Nicolin