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Date: Fri, 14 Jun 2013 08:21:06 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: bhelgaas@...gle.com
Cc: linux-pci@...r.kernel.org, ddutile@...hat.com,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] pci: Enable overrides for missing ACS capabilities
Bump. Comments?
On Thu, 2013-05-30 at 12:40 -0600, Alex Williamson wrote:
> PCIe ACS (Access Control Services) is the PCIe 2.0+ feature that
> allows us to control whether transactions are allowed to be redirected
> in various subnodes of a PCIe topology. For instance, if two
> endpoints are below a root port or downsteam switch port, the
> downstream port may optionally redirect transactions between the
> devices, bypassing upstream devices. The same can happen internally
> on multifunction devices. The transaction may never be visible to the
> upstream devices.
>
> One upstream device that we particularly care about is the IOMMU. If
> a redirection occurs in the topology below the IOMMU, then the IOMMU
> cannot provide isolation between devices. This is why the PCIe spec
> encourages topologies to include ACS support. Without it, we have to
> assume peer-to-peer DMA within a hierarchy can bypass IOMMU isolation.
>
> Unfortunately, far too many topologies do not support ACS to make this
> a steadfast requirement. Even the latest chipsets from Intel are only
> sporadically supporting ACS. We have trouble getting interconnect
> vendors to include the PCIe spec required PCIe capability, let alone
> suggested features.
>
> Therefore, we need to add some flexibility. The pcie_acs_override=
> boot option lets users opt-in specific devices or sets of devices to
> assume ACS support. The "downstream" option assumes full ACS support
> on root ports and downstream switch ports. The "multifunction"
> option assumes the subset of ACS features available on multifunction
> endpoints and upstream switch ports are supported. The "id:nnnn:nnnn"
> option enables ACS support on devices matching the provided vendor
> and device IDs, allowing more strategic ACS overrides. These options
> may be combined in any order. A maximum of 16 id specific overrides
> are available. It's suggested to use the most limited set of options
> necessary to avoid completely disabling ACS across the topology.
>
> Note to hardware vendors, we have facilities to permanently quirk
> specific devices which enforce isolation but not provide an ACS
> capability. Please contact me to have your devices added and save
> your customers the hassle of this boot option.
>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
> Documentation/kernel-parameters.txt | 10 +++
> drivers/pci/quirks.c | 102 +++++++++++++++++++++++++++++++++++
> 2 files changed, 112 insertions(+)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 47bb23c..a60e6ad 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2349,6 +2349,16 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> nomsi Do not use MSI for native PCIe PME signaling (this makes
> all PCIe root ports use INTx for all services).
>
> + pcie_acs_override =
> + [PCIE] Override missing PCIe ACS support for:
> + downstream
> + All downstream ports - full ACS capabilties
> + multifunction
> + All multifunction devices - multifunction ACS subset
> + id:nnnn:nnnn
> + Specfic device - full ACS capabilities
> + Specified as vid:did (vendor/device ID) in hex
> +
> pcmv= [HW,PCMCIA] BadgePAD 4
>
> pd. [PARIDE]
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 0369fb6..c7609f6 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -3292,11 +3292,113 @@ struct pci_dev *pci_get_dma_source(struct pci_dev *dev)
> return pci_dev_get(dev);
> }
>
> +static bool acs_on_downstream;
> +static bool acs_on_multifunction;
> +
> +#define NUM_ACS_IDS 16
> +struct acs_on_id {
> + unsigned short vendor;
> + unsigned short device;
> +};
> +static struct acs_on_id acs_on_ids[NUM_ACS_IDS];
> +static u8 max_acs_id;
> +
> +static __init int pcie_acs_override_setup(char *p)
> +{
> + if (!p)
> + return -EINVAL;
> +
> + while (*p) {
> + if (!strncmp(p, "downstream", 10))
> + acs_on_downstream = true;
> + if (!strncmp(p, "multifunction", 13))
> + acs_on_multifunction = true;
> + if (!strncmp(p, "id:", 3)) {
> + char opt[5];
> + int ret;
> + long val;
> +
> + if (max_acs_id >= NUM_ACS_IDS - 1) {
> + pr_warn("Out of PCIe ACS override slots (%d)\n",
> + NUM_ACS_IDS);
> + goto next;
> + }
> +
> + p += 3;
> + snprintf(opt, 5, "%s", p);
> + ret = kstrtol(opt, 16, &val);
> + if (ret) {
> + pr_warn("PCIe ACS ID parse error %d\n", ret);
> + goto next;
> + }
> + acs_on_ids[max_acs_id].vendor = val;
> +
> + p += strcspn(p, ":");
> + if (*p != ':') {
> + pr_warn("PCIe ACS invalid ID\n");
> + goto next;
> + }
> +
> + p++;
> + snprintf(opt, 5, "%s", p);
> + ret = kstrtol(opt, 16, &val);
> + if (ret) {
> + pr_warn("PCIe ACS ID parse error %d\n", ret);
> + goto next;
> + }
> + acs_on_ids[max_acs_id].device = val;
> + max_acs_id++;
> + }
> +next:
> + p += strcspn(p, ",");
> + if (*p == ',')
> + p++;
> + }
> +
> + if (acs_on_downstream || acs_on_multifunction || max_acs_id)
> + pr_warn("Warning: PCIe ACS overrides enabled; This may allow non-IOMMU protected peer-to-peer DMA\n");
> +
> + return 0;
> +}
> +early_param("pcie_acs_override", pcie_acs_override_setup);
> +
> +static int pcie_acs_overrides(struct pci_dev *dev, u16 acs_flags)
> +{
> + int i;
> +
> + /* Never override ACS for legacy devices or devices with ACS caps */
> + if (!pci_is_pcie(dev) ||
> + pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS))
> + return -ENOTTY;
> +
> + for (i = 0; i < max_acs_id; i++)
> + if (acs_on_ids[i].vendor == dev->vendor &&
> + acs_on_ids[i].device == dev->device)
> + return 1;
> +
> + switch (pci_pcie_type(dev)) {
> + case PCI_EXP_TYPE_DOWNSTREAM:
> + case PCI_EXP_TYPE_ROOT_PORT:
> + if (acs_on_downstream)
> + return 1;
> + break;
> + case PCI_EXP_TYPE_ENDPOINT:
> + case PCI_EXP_TYPE_UPSTREAM:
> + case PCI_EXP_TYPE_LEG_END:
> + case PCI_EXP_TYPE_RC_END:
> + if (acs_on_multifunction && dev->multifunction)
> + return 1;
> + }
> +
> + return -ENOTTY;
> +}
> +
> static const struct pci_dev_acs_enabled {
> u16 vendor;
> u16 device;
> int (*acs_enabled)(struct pci_dev *dev, u16 acs_flags);
> } pci_dev_acs_enabled[] = {
> + { PCI_ANY_ID, PCI_ANY_ID, pcie_acs_overrides },
> { 0 }
> };
>
>
--
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