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SubjectRe: [PATCH V2] PCI: Enable PASID when End-to-End TLP is supported by all bridges
On Tue, Jun 19, 2018 at 10:14:46PM -0400, Sinan Kaya wrote:
> A PCIe endpoint carries the process address space identifier (PASID) in
> the TLP prefix as part of the memory read/write transaction. The address
> information in the TLP is relevant only for a given PASID context.
>
> An IOMMU takes PASID value and the address information from the
> TLP to look up the physical address in the system.
>
> If a bridge drops the TLP prefix, the translation agent can resolve the
> address to an incorrect location and cause data corruption. Prevent
> this condition by requiring End-to-End TLP prefix to be supported on the
> entire data path between the endpoint and the root port.

PASID is an End-End TLP Prefix (PCIe r4.0, sec 6.20). Sec 2.2.10.2 says

It is an error to receive a TLP with an End-End TLP Prefix by a
Receiver that does not support End-End TLP Prefixes. A TLP in
violation of this rule is handled as a Malformed TLP. This is a
reported error associated with the Receiving Port (see Section 6.2).

So I agree that we shouldn't enable PASID in an endpoint unless all
the switch ports leading to it support End-End prefixes. But I don't
see how a bridge can drop a prefix and cause data corruption -- if it
doesn't support End-End prefixes, shouldn't the bridge raise a
Malformed TLP error instead of forwarding the TLP?

> Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
> ---
> drivers/pci/ats.c | 9 +++++++++
> drivers/pci/probe.c | 17 +++++++++++++++++
> include/linux/pci.h | 1 +
> include/uapi/linux/pci_regs.h | 1 +
> 4 files changed, 28 insertions(+)
>
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index 4923a2a..e1b2e6d 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -268,6 +268,7 @@ EXPORT_SYMBOL_GPL(pci_reset_pri);
> int pci_enable_pasid(struct pci_dev *pdev, int features)
> {
> u16 control, supported;
> + struct pci_dev *bridge;
> int pos;
>
> if (WARN_ON(pdev->pasid_enabled))
> @@ -277,6 +278,14 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
> if (!pos)
> return -EINVAL;
>
> + bridge = pci_upstream_bridge(pdev);
> + while (bridge) {
> + if (!bridge->eetlp_prefix)
> + return -EINVAL;
> +
> + bridge = pci_upstream_bridge(bridge);
> + }

I was hoping to avoid even this loop by having the eetlp_prefix bit
indicate that "End-End TLP Prefixes are supported from the Root Port
to here".

> pci_read_config_word(pdev, pos + PCI_PASID_CAP, &supported);
> supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ac876e3..a7f7ac1 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2042,6 +2042,22 @@ static void pci_configure_ltr(struct pci_dev *dev)
> #endif
> }
>
> +static void pci_configure_eetlp_prefix(struct pci_dev *dev)
> +{
> +#ifdef CONFIG_PCI_PASID
> + u32 cap;
> +
> + if (!pci_is_pcie(dev))
> + return;
> +
> + pcie_capability_read_dword(dev, PCI_EXP_DEVCAP2, &cap);
> + if (!(cap & PCI_EXP_DEVCAP2_E2ETLP))
> + return;
> +
> + dev->eetlp_prefix = 1;

I.e., here we would do:

if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
dev->eetlp_prefix_path = 1;
else {
bridge = pci_upstream_bridge(dev);
if (bridge && bridge->eetlp_prefix_path)
dev->eetlp_prefix_path = 1;
}

> +#endif
> +}
> +
> static void pci_configure_device(struct pci_dev *dev)
> {
> struct hotplug_params hpp;
> @@ -2051,6 +2067,7 @@ static void pci_configure_device(struct pci_dev *dev)
> pci_configure_extended_tags(dev, NULL);
> pci_configure_relaxed_ordering(dev);
> pci_configure_ltr(dev);
> + pci_configure_eetlp_prefix(dev);
>
> memset(&hpp, 0, sizeof(hpp));
> ret = pci_get_hp_params(dev, &hpp);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 340029b..cf88d47 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -350,6 +350,7 @@ struct pci_dev {
> unsigned int ltr_path:1; /* Latency Tolerance Reporting
> supported from root to here */
> #endif
> + unsigned int eetlp_prefix:1; /* End-to-End TLP Prefix */
>
> pci_channel_state_t error_state; /* Current connectivity state */
> struct device dev; /* Generic device interface */
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index 4da87e2..a617ab2 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -636,6 +636,7 @@
> #define PCI_EXP_DEVCAP2_OBFF_MASK 0x000c0000 /* OBFF support mechanism */
> #define PCI_EXP_DEVCAP2_OBFF_MSG 0x00040000 /* New message signaling */
> #define PCI_EXP_DEVCAP2_OBFF_WAKE 0x00080000 /* Re-use WAKE# for OBFF */
> +#define PCI_EXP_DEVCAP2_E2ETLP 0x00200000 /* End-to-End TLP Prefix */

It looks like lspci doesn't decode this bit (and several others in
DevCap2). Would you be interested in adding that? The source is at
git://git.kernel.org/pub/scm/utils/pciutils/pciutils.git

> #define PCI_EXP_DEVCTL2 40 /* Device Control 2 */
> #define PCI_EXP_DEVCTL2_COMP_TIMEOUT 0x000f /* Completion Timeout Value */
> #define PCI_EXP_DEVCTL2_COMP_TMOUT_DIS 0x0010 /* Completion Timeout Disable */
> --
> 2.7.4
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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