Re: nested-smmuv3 topic, Sep 2024

[Mostafa Saleh <smostafa@google.com>]

Hi Nicolin,

On Thu, Sep 05, 2024 at 01:26:20AM -0700, Nicolin Chen wrote:
> Hi all,
> 
> Hope I didn't miss anybody who is related to the topic. Please,
> feel free to add!
> 
> <--- Background --->
> As some of you know, there is an ongoing effort for nested-smmuv3
> support in QEMU on ARM, working with the kernel IOMMUFD uAPIs:
> [Nesting for vSTE]
> https://lore.kernel.org/linux-iommu/0-v2-621370057090+91fec-smmuv3_nesting_jgg@nvidia.com/
> [Nesting for invalidations]
> https://lore.kernel.org/linux-iommu/cover.1724776335.git.nicolinc@nvidia.com/
> 
> The kernel patches are still under review. Jason and I are hoping
> them to get merged at next cycle for v6.13, which means the QEMU
> patches might start a review process as early as Nov/Dec?
> 
> That being said, I think we are way behind the point that patches
> can get reviewed: most of the QEMU patches on my branches weren't
> touched very often, but merely updated to the latest kernel uAPIs
> for verification. So, I feel this might be a good point to gather
> folks together to discuss about the possible timeline and ask for
> help. I think this would potentially help folks who are going to
> attend the KVM forum (or LPC) to carry out a discussion. (Sorry,
> I won't make it due to some conflict..)
> 
> <-- Task Breakdown --->
> I previously sent a RFCv1 series collecting comments/suggestions,
> for multi-vSMMU instance design in ARM Virt code:
> https://lore.kernel.org/qemu-devel/cover.1719361174.git.nicolinc@nvidia.com/
> (And thanks again for all the inputs!)
> 
> 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
> 
> 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.

I don’t have plans to work on qemu in the next months, most of my
upstream focus will be on pKVM SMMUv3 support[1] in Linux which might
overlap with some of the vSMMU work but in the kernel side.

Otherwise, I’d be happy to review patches.

[1] https://lore.kernel.org/kvmarm/20230201125328.2186498-1-jean-philippe@linaro.org/

Thanks,
Mostafa

> 
> 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..
> 
> Thank you
> Nicolin