linux-kernel - Re: [PATCH 3/7] iommu/vt-d: Enhance compatibility check for paging domain attach

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Message-ID: <20241015124849.GJ1825128@ziepe.ca>
Date: Tue, 15 Oct 2024 09:48:49 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: iommu@...ts.linux.dev, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
	Vasant Hegde <vasant.hegde@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] iommu/vt-d: Enhance compatibility check for paging
 domain attach

On Tue, Oct 15, 2024 at 10:52:19AM +0800, Baolu Lu wrote:
> On 2024/10/15 3:24, Jason Gunthorpe wrote:
> > On Mon, Oct 14, 2024 at 09:25:03AM +0800, Baolu Lu wrote:
> > > > > +	if (domain->type & __IOMMU_DOMAIN_PAGING) {
> > > > It looks like this entire function is already never called for
> > > > anything but paging?
> > > > 
> > > > The only three callers are:
> > > > 
> > > > 	.default_domain_ops = &(const struct iommu_domain_ops) {
> > > > 		.attach_dev		= intel_iommu_attach_device,
> > > > 		.set_dev_pasid		= intel_iommu_set_dev_pasid,
> > > > 
> > > > and
> > > > 
> > > > static const struct iommu_domain_ops intel_nested_domain_ops = {
> > > > 	.attach_dev		= intel_nested_attach_dev,
> > > > 
> > > > And none of those cases can be anything except a paging domain by
> > > > definition.
> > > A nested domain is not a paging domain. It represents a user-space page
> > > table that nested on a parent paging domain. Perhaps I overlooked
> > > anything?
> > It only calls it on the s2_parent which is always a paging domain?
> > 
> > 	ret = prepare_domain_attach_device(&dmar_domain->s2_domain->domain, dev);
> 
> Yea, you are right. I overlooked that part.  I'll remove the 'if'
> statement and utilize a WARN_ON() function instead.
> 
> And also, I will rename this function with a meaningful name,some like
> paging_domain_is_compatible()?

That sounds good too

Ultimately you want to try to structure the driver so that there is a
struct paging_domain that is always the paging domain type and
everything is easy to understand. Don't re-use the same struct for
identity/blocked/nested domains.

Jason