linux-kernel - Re: [PATCH] PCI: ACPI: Allow internal devices to be marked as untrusted

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Message-ID: <YfeEoF35RPDVMdzD@lahna>
Date:   Mon, 31 Jan 2022 08:41:36 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Rajat Jain <rajatja@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rajat Jain <rajatxjain@...il.com>,
        Dmitry Torokhov <dtor@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Pavel Machek <pavel@...x.de>,
        Oliver O'Halloran <oohall@...il.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] PCI: ACPI: Allow internal devices to be marked as
 untrusted

Hi,

On Sun, Jan 30, 2022 at 03:30:39PM +0100, Rafael J. Wysocki wrote:
> > I'm open to doing so if the others also feel the same way. IMHO
> > though, the semantics of ACPI "DmaProperty" differ from the semantics
> > of the property I'm proposing here.
> >
> > The current (documented) semantics (of "DmaProperty"): *This device
> > (root port) is trusted*, but any devices downstream are not to be
> > trusted.
> >
> > What I need and am proposing (new "UntrustedDevice"): *This device as
> > well as any downstream devices* are untrusted.
> >
> > Note that there may be firmware implementing "DmaProperty" already out
> > there (for windows), and if we decide to use it for my purposes, then
> > there shall be a discrepancy in how Linux uses that property vs
> > Windows. Is that acceptable?
> 
> It may be confusing, so I'd rather not do that.
> 
> The platform firmware will use it with the Windows use case in mind
> and if it has side effects in Linux, problems are likely to appear in
> the field.
> 
> So the question is rather not about it being acceptable, but about
> whether or not this is generally going to work.

I was kind of implying that we could perhaps contact Microsoft and ask
them if the wording could be changed to cover all the devices, not just
PCIe root ports. I think this is something they will also need for
things like internal WI-FI controllers.

If that's not possible then no objections adding "UntrustedDevice". We
just need to deal with the "DmaProperty" anyway and both end up setting
pdev->untrusted in the similar manner.