linux-kernel - Re: [PATCH 7/8] iommu/amd: Add support for nested domain allocation

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Message-ID: <20250822211618.GF1405994@nvidia.com>
Date: Fri, 22 Aug 2025 18:16:18 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	linux-kernel@...r.kernel.org, robin.murphy@....com, will@...nel.org,
	joro@...tes.org, kevin.tian@...el.com, jsnitsel@...hat.com,
	vasant.hegde@....com, iommu@...ts.linux.dev, santosh.shukla@....com,
	sairaj.arunkodilkar@....com, jon.grimm@....com,
	prashanthpra@...gle.com, wvw@...gle.com, wnliu@...gle.com,
	gptran@...gle.com, kpsingh@...gle.com
Subject: Re: [PATCH 7/8] iommu/amd: Add support for nested domain allocation

On Fri, Aug 22, 2025 at 12:51:02PM -0700, Nicolin Chen wrote:
> > @@ -3113,6 +3116,7 @@ const struct iommu_ops amd_iommu_ops = {
> >  	.release_domain = &release_domain,
> >  	.identity_domain = &identity_domain.domain,
> >  	.domain_alloc_paging_flags = amd_iommu_domain_alloc_paging_flags,
> > +	.domain_alloc_nested = amd_iommu_domain_alloc_nested,
> >  	.domain_alloc_sva = amd_iommu_domain_alloc_sva,
> >  	.probe_device = amd_iommu_probe_device,
> >  	.release_device = amd_iommu_release_device,
> 
> This will be an HWPT-based nesting support, v.s. vIOMMU-based.
> 
> If AMD wants to enable its Command/Event Buffers, I think this
> should follow the vIOMMU model instead.

I've been expecting drivers to do both, like ARM.. Nested is the basic
infrastructure and then the viommu changes what domain id nested will
use similar to how ARM constrains the VMID based on the viommu.

Suravee is this how you see AMD evolving as well?

Jason