linux-kernel - Re: [PATCH v2 09/12] iommu/amd: Add support for nest parent domain allocation

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Message-ID: <20251006144319.GR3360665@nvidia.com>
Date: Mon, 6 Oct 2025 11:43:19 -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, joao.m.martins@...cle.com,
	alejandro.j.jimenez@...cle.com
Subject: Re: [PATCH v2 09/12] iommu/amd: Add support for nest parent domain
 allocation

On Thu, Oct 02, 2025 at 11:00:14AM -0700, Nicolin Chen wrote:

> >  	switch (flags & supported_flags) {
> >  	case IOMMU_HWPT_ALLOC_DIRTY_TRACKING:
> > -		/* Allocate domain with v1 page table for dirty tracking */
> > -		if (!amd_iommu_hd_support(iommu))
> > +	case IOMMU_HWPT_ALLOC_NEST_PARENT:
> > +	case IOMMU_HWPT_ALLOC_DIRTY_TRACKING | IOMMU_HWPT_ALLOC_NEST_PARENT:
> > +		/*
> > +		 * Allocate domain with v1 page table for dirty tracking
> > +		 * and/or Nest parent.
> > +		 */
> > +		if ((flags & IOMMU_HWPT_ALLOC_DIRTY_TRACKING) &&
> > +		    !amd_iommu_hd_support(iommu))
> >  			break;
> 
> And add here:
> 		if ((flags & IOMMU_HWPT_ALLOC_NEST_PARENT)) &&
> 		    !is_nest_parent_supported())
> 			    break;

Yeah this looks better

On VT-D we have V1/V2 specific alloc functions and these tests were
put at the top of those functions in this form. This is close enough,
it is helpful to be consistent.

Jason