Re: [RFC v1 0/5] Hyper-V: Add para-virtualized IOMMU support for Linux guests

[Yu Zhang]

On Thu, Jan 08, 2026 at 06:45:52PM +0000, Michael Kelley wrote:
> From: Yu Zhang <zhangyu1@xxxxxxxxxxxxxxxxxxx> Sent: Monday, December 8, 2025 9:11 PM
> > 
> > This patch series introduces a para-virtualized IOMMU driver for
> > Linux guests running on Microsoft Hyper-V. The primary objective
> > is to enable hardware-assisted DMA isolation and scalable device
> 
> Is there any particular meaning for the qualifier "scalable" vs. just
> "device assignment"? I just want to understand what you are getting
> at.
> 

Sorry for the ambiguity.
I intended to highlight two primary use cases for pvIOMMU:
- to enable in-kernel DMA protection within the guest.
- to allow device assignment to guest user space (e.g., via VFIO).

I avoided using the phrase "device assignment" alone, because people may be
confused if the main purpose of introducing pvIOMMU is for device assignment
to a L1 guest(which actually does not depend on any virtual IOMMU) or to a
L2 nested guest(altough I guess w/ pvIOMMU, it should work but we've never
tested that case and are not aware any such requirement).

And you are right, simply adding "scalable" didn't help clarify this.
I will rephrase the commit message. Thanks!

B.R.
Yu