Re: [PATCH V2] PCI: Enable PASID when End-to-End TLP is supported by all bridges

[Bjorn Helgaas]

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@xxxxxxxxxxxxxx>
> ---
>  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
> 
> 
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