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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Tue, 25 Jan 2022 15:45:03 +0100
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Subject: Re: [PATCH] PCI: ACPI: Allow internal devices to be marked as untrusted
To:     Mika Westerberg <mika.westerberg@linux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Rajat Jain <rajatja@google.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rajat Jain <rajatxjain@gmail.com>,
        Dmitry Torokhov <dtor@google.com>,
        Jesse Barnes <jsbarnes@google.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Pavel Machek <pavel@denx.de>,
        "Oliver O'Halloran" <oohall@gmail.com>,
        Joerg Roedel <joro@8bytes.org>
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On Tue, Jan 25, 2022 at 1:55 PM Mika Westerberg
<mika.westerberg@linux.intel.com> wrote:
>
> On Tue, Jan 25, 2022 at 12:15:02PM +0100, Greg Kroah-Hartman wrote:
> > On Tue, Jan 25, 2022 at 12:58:52PM +0200, Mika Westerberg wrote:
> > > On Mon, Jan 24, 2022 at 08:27:17AM +0200, Mika Westerberg wrote:
> > > > > > This patch introduces a new "UntrustedDevice" property that can be used
> > > > > > by the firmware to mark any device as untrusted.
> > > >
> > > > I think this new property should be documented somewhere too (also
> > > > explain when to use it instead of ExternalFacingPort). If not in the
> > > > next ACPI spec or some supplemental doc then perhaps in the DT bindings
> > > > under Documentation/devicetree/bindings.
> > >
> > > Actually Microsoft has similar already:
> > >
> > > https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-internal-pcie-ports-accessible-to-users-and-requiring-dma-protection
> > >
> > > I think we should use that too here.
> >
> > But we do not have "dma protection" for Linux, so how will that value
> > make sense?
>
> Yes I think we do - IOMMU. That's the same thing what we do now for
> "External Facing Ports". This one just is for internal ones.
>
> > And shouldn't this be an ACPI standard?
>
> Probably should or some supplemental doc but not sure how easy these
> "properties" can be added there to be honest.
>
> Some of these that we use in Linux too are from that same page:
>
> https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports
>
> Namely these: HotPlugSupportInD3, ExternalFacingPort, usb4-host-interface,
> usb4-port-number and StorageD3Enable.

Right.

We are kind of on the receiving end here, because at the time we learn
about these things the decisions to use them have been made already.