linux-kernel - Re: [PATCH] pci: Rename pci_dev->untrusted to pci

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Date:   Tue, 20 Apr 2021 12:07:08 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Rajat Jain <rajatja@...gle.com>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, rajatxjain@...il.com
Subject: Re: [PATCH] pci: Rename pci_dev->untrusted to pci_dev->external

On Tue, Apr 20, 2021 at 07:10:06AM +0100, Christoph Hellwig wrote:
> On Mon, Apr 19, 2021 at 05:30:49PM -0700, Rajat Jain wrote:
> > The current flag name "untrusted" is not correct as it is populated
> > using the firmware property "external-facing" for the parent ports. In
> > other words, the firmware only says which ports are external facing, so
> > the field really identifies the devices as external (vs internal).
> > 
> > Only field renaming. No functional change intended.
> 
> I don't think this is a good idea.  First the field should have been
> added to the generic struct device as requested multiple times before.

Fair point.  There isn't anything PCI-specific about this idea.  The
ACPI "ExternalFacingPort" and DT "external-facing" are currently only
defined for PCI devices, but could be applied elsewhere.

> Right now this requires horrible hacks in the IOMMU code to get at the
> pci_dev, and also doesn't scale to various other potential users.

Agreed, this is definitely suboptimal.  Do you have other users in
mind?  Maybe they could help inform the plan.

> Second the untrusted is objectively a better name.  Because untrusted
> is how we treat the device, which is what mattes.  External is just
> how we come to that conclusion.

The decision to treat "external" as being "untrusted" is a little bit
of policy that the PCI core really doesn't care about, so I think it
does make some sense to let the places that *do* care decide what to
trust based on "external" and possibly other factors, e.g., whether
the device is a BMC or processes untrusted data, etc.

But I guess it makes sense to wait until we have a better motivation
before renaming it, since we don't gain any functionality here.

Bjorn