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    SubjectRe: [PATCH v2 2/7] PCI: Set "untrusted" flag for truly external devices only
    Hello,

    On Mon, Jul 6, 2020 at 9:38 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
    >
    > On Mon, Jun 29, 2020 at 09:49:38PM -0700, Rajat Jain wrote:
    > > The "ExternalFacing" devices (root ports) are still internal devices that
    > > sit on the internal system fabric and thus trusted. Currently they were
    > > being marked untrusted.
    > >
    > > This patch uses the platform flag to identify the external facing devices
    > > and then use it to mark any downstream devices as "untrusted". The
    > > external-facing devices themselves are left as "trusted". This was
    > > discussed here: https://lkml.org/lkml/2020/6/10/1049
    >
    > Use the imperative mood in the commit log, as you did for 1/7. E.g.,
    > instead of "This patch uses ...", say "Use the platform flag ...".
    > That helps all the commit logs read nicely together.
    >
    > I think this patch makes two changes that should be separated:
    >
    > - Treat "external-facing" devices as internal.
    >
    > - Look for the "external-facing" or "ExternalFacing" property on
    > Switch Downstream Ports as well as Root Ports.
    >
    > > Signed-off-by: Rajat Jain <rajatja@google.com>
    > > ---
    > > v2: cosmetic changes in commit log
    > >
    > > drivers/iommu/intel/iommu.c | 2 +-
    > > drivers/pci/of.c | 2 +-
    > > drivers/pci/pci-acpi.c | 13 +++++++------
    > > drivers/pci/probe.c | 2 +-
    > > include/linux/pci.h | 8 ++++++++
    > > 5 files changed, 18 insertions(+), 9 deletions(-)
    > >
    > > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
    > > index d759e7234e982..1ccb224f82496 100644
    > > --- a/drivers/iommu/intel/iommu.c
    > > +++ b/drivers/iommu/intel/iommu.c
    > > @@ -4743,7 +4743,7 @@ static inline bool has_untrusted_dev(void)
    > > struct pci_dev *pdev = NULL;
    > >
    > > for_each_pci_dev(pdev)
    > > - if (pdev->untrusted)
    > > + if (pdev->untrusted || pdev->external_facing)
    >
    > I think checking pdev->external_facing is enough for this case,
    > because it's impossible to have pdev->untrusted unless a parent has
    > pdev->external_facing.

    Agree.

    >
    > IIUC, this usage is asking "might we ever have an external device?"
    > as opposed to the "pdev->untrusted" uses, which are asking "is *this*
    > device an external device?"

    Agree.

    >
    > > return true;
    > >
    > > return false;
    > > diff --git a/drivers/pci/of.c b/drivers/pci/of.c
    > > index 27839cd2459f6..22727fc9558df 100644
    > > --- a/drivers/pci/of.c
    > > +++ b/drivers/pci/of.c
    > > @@ -42,7 +42,7 @@ void pci_set_bus_of_node(struct pci_bus *bus)
    > > } else {
    > > node = of_node_get(bus->self->dev.of_node);
    > > if (node && of_property_read_bool(node, "external-facing"))
    > > - bus->self->untrusted = true;
    > > + bus->self->external_facing = true;
    > > }
    > >
    > > bus->dev.of_node = node;
    > > diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
    > > index 7224b1e5f2a83..492c07805caf8 100644
    > > --- a/drivers/pci/pci-acpi.c
    > > +++ b/drivers/pci/pci-acpi.c
    > > @@ -1213,22 +1213,23 @@ static void pci_acpi_optimize_delay(struct pci_dev *pdev,
    > > ACPI_FREE(obj);
    > > }
    > >
    > > -static void pci_acpi_set_untrusted(struct pci_dev *dev)
    > > +static void pci_acpi_set_external_facing(struct pci_dev *dev)
    > > {
    > > u8 val;
    > >
    > > - if (pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT)
    > > + if (pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT &&
    > > + pci_pcie_type(dev) != PCI_EXP_TYPE_DOWNSTREAM)
    >
    > This looks like a change worthy of its own patch. We used to look for
    > "ExternalFacingPort" only on Root Ports; now we'll also do it for
    > Switch Downstream Ports.

    Can do. (please see below)

    >
    > Can you include DT and ACPI spec references if they exist? I found
    > this mention:
    > https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports
    > which actually says it should only be implemented for Root Ports.

    I actually have no references. It seems to me that the microsoft spec
    assumes that all external ports must be implemented on root ports, but
    I think it would be equally fair for systems with PCIe switches to
    implement one on one of their switch downstream ports. I don't have an
    immediate use of this anyway, so if you think this should rather wait
    unless someone really has this case, this can wait. Let me know.

    >
    > It also mentions a "DmaProperty" that looks related. Maybe Linux
    > should also pay attention to this?

    Interesting. Since this is not in use currently by the kernel as well
    as not exposed by (our) BIOS, I don't have an immediate use case for
    this. I'd like to defer this for later (as-the-need-arises).

    >
    > If we do change this, should we use pcie_downstream_port(), which
    > includes PCI-to-PCIe bridges as well?

    Sure, can do that.

    >
    > > return;
    > > if (device_property_read_u8(&dev->dev, "ExternalFacingPort", &val))
    > > return;
    > >
    > > /*
    > > - * These root ports expose PCIe (including DMA) outside of the
    > > - * system so make sure we treat them and everything behind as
    > > + * These root/down ports expose PCIe (including DMA) outside of the
    > > + * system so make sure we treat everything behind them as
    > > * untrusted.
    > > */
    > > if (val)
    > > - dev->untrusted = 1;
    > > + dev->external_facing = 1;
    > > }
    > >
    > > static void pci_acpi_setup(struct device *dev)
    > > @@ -1240,7 +1241,7 @@ static void pci_acpi_setup(struct device *dev)
    > > return;
    > >
    > > pci_acpi_optimize_delay(pci_dev, adev->handle);
    > > - pci_acpi_set_untrusted(pci_dev);
    > > + pci_acpi_set_external_facing(pci_dev);
    > > pci_acpi_add_edr_notifier(pci_dev);
    > >
    > > pci_acpi_add_pm_notifier(adev, pci_dev);
    > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
    > > index 6d87066a5ecc5..8c40c00413e74 100644
    > > --- a/drivers/pci/probe.c
    > > +++ b/drivers/pci/probe.c
    > > @@ -1552,7 +1552,7 @@ static void set_pcie_untrusted(struct pci_dev *dev)
    > > * untrusted as well.
    > > */
    > > parent = pci_upstream_bridge(dev);
    > > - if (parent && parent->untrusted)
    > > + if (parent && (parent->untrusted || parent->external_facing))
    > > dev->untrusted = true;
    > > }
    > >
    > > diff --git a/include/linux/pci.h b/include/linux/pci.h
    > > index a26be5332bba6..fe1bc603fda40 100644
    > > --- a/include/linux/pci.h
    > > +++ b/include/linux/pci.h
    > > @@ -432,6 +432,14 @@ struct pci_dev {
    > > * mappings to make sure they cannot access arbitrary memory.
    > > */
    > > unsigned int untrusted:1;
    > > + /*
    > > + * Devices are marked as external-facing using info from platform
    > > + * (ACPI / devicetree). An external-facing device is still an internal
    > > + * trusted device, but it faces external untrusted devices. Thus any
    > > + * devices enumerated downstream an external-facing device is marked
    > > + * as untrusted.
    >
    > This comment has a subject/verb agreement problem.

    I assume you meant s/is/are/ in last sentence. Will do.

    Thanks,

    Rajat


    >
    > > + */
    > > + unsigned int external_facing:1;
    > > unsigned int broken_intx_masking:1; /* INTx masking can't be used */
    > > unsigned int io_window_1k:1; /* Intel bridge 1K I/O windows */
    > > unsigned int irq_managed:1;
    > > --
    > > 2.27.0.212.ge8ba1cc988-goog
    > >

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