linux-kernel - Re: [PATCH 4/4] pci: export untrusted attribute in sysfs

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Message-ID: <CACK8Z6FecYkAYQh4sm4RbAQ1iwb9gexqgY9ExD9BH2p-5Usj=g@mail.gmail.com>
Date:   Wed, 17 Jun 2020 12:53:03 -0700
From:   Rajat Jain <rajatja@...gle.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, iommu@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-acpi@...r.kernel.org, Raj Ashok <ashok.raj@...el.com>,
        "Krishnakumar, Lalithambika" <lalithambika.krishnakumar@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Prashant Malani <pmalani@...gle.com>,
        Benson Leung <bleung@...gle.com>,
        Todd Broch <tbroch@...gle.com>,
        Alex Levin <levinale@...gle.com>,
        Mattias Nissler <mnissler@...gle.com>,
        Rajat Jain <rajatxjain@...il.com>,
        Bernie Keany <bernie.keany@...el.com>,
        Aaron Durbin <adurbin@...gle.com>,
        Diego Rivas <diegorivas@...gle.com>,
        Duncan Laurie <dlaurie@...gle.com>,
        Furquan Shaikh <furquan@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Christian Kellner <christian@...lner.me>,
        Alex Williamson <alex.williamson@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Oliver O'Halloran" <oohall@...il.com>
Subject: Re: [PATCH 4/4] pci: export untrusted attribute in sysfs

Hi Greg, Christoph,

On Wed, Jun 17, 2020 at 12:31 AM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Tue, Jun 16, 2020 at 12:27:35PM -0700, Rajat Jain wrote:
> > Need clarification. The flag "untrusted" is currently a part of
> > pci_dev struct, and is populated within the PCI subsystem.
>
> Yes, and that is the problem.
>
> >
> > 1) Is your suggestion to move this flag as well as the attribute to
> > device core (in "struct device")? This would allow other buses to
> > populate/use this flag if they want. By default it'll be set to 0 for
> > all devices (PCI subsystem will populate it based on platform info,
> > like it does today).
> >
> > OR
> >
> > 2) Are you suggesting to keep the "untrusted" flag within PCI, but
> > attach the sysfs attribute to the base device? (&pci_dev->dev)?
>
> (1).  As for IOMMUs and userspace policy it really should not matter
> what bus a device is on if it is external and not trustworthy.

Sure. I can move the flag to the "struct device" (and likely call
it "external" instead of "untrusted" so as to make it suitable for
more use cases later).  The buses can fill this up if they know which
devices are external and which ones are not (otherwise it will be 0 by
default). The PCI can fill this up like it does today, from platform
info (ACPI / Device tree). Greg, how does this sound?

Thanks,

Rajat