On Thu, Apr 18, 2019 at 01:58:59PM +0200, Christian König wrote:
> A lot of root complexes can still do P2P even when PCI devices
> don't share a common upstream bridge.
>
> Start adding a whitelist and allow P2P if both participants are
> attached to known good root complex.
Is there a plan for addressing this in a generic way that doesn't
require an OS modification for every new "known good root complex",
e.g., some PCIe or ACPI spec update that allows the OS to discover
this?
> Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> ---
> drivers/pci/p2pdma.c | 38 +++++++++++++++++++++++++++++++++++---
> 1 file changed, 35 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index c52298d76e64..212baaa7f93b 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -274,6 +274,31 @@ static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
> seq_buf_printf(buf, "%s;", pci_name(pdev));
> }
>
> +/*
> + * If we can't find a common upstream bridge take a look at the root complex and
> + * compare it to a whitelist of known good hardware.
> + */
> +static bool root_complex_whitelist(struct pci_dev *dev)
> +{
> + struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
> + struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
> + unsigned short vendor, device;
> +
> + if (!root)
> + return false;
> +
> + vendor = root->vendor;
> + device = root->device;
> + pci_dev_put(root);
> +
> + /* AMD ZEN host bridges can do peer to peer */
> + if (vendor == PCI_VENDOR_ID_AMD && device == 0x1450)
> + return true;
> +
> + /* TODO: Extend that to a proper whitelist */
> + return false;
> +}
> +
> /*
> * Find the distance through the nearest common upstream bridge between
> * two PCI devices.
> @@ -317,13 +342,13 @@ static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
> * In this case, a list of all infringing bridge addresses will be
> * populated in acs_list (assuming it's non-null) for printk purposes.
> */
> -static int upstream_bridge_distance(struct pci_dev *a,
> - struct pci_dev *b,
> +static int upstream_bridge_distance(struct pci_dev *provider,
> + struct pci_dev *client,
> struct seq_buf *acs_list)
> {
> + struct pci_dev *a = provider, *b = client, *bb;
> int dist_a = 0;
> int dist_b = 0;
> - struct pci_dev *bb = NULL;
> int acs_cnt = 0;
>
> /*
> @@ -354,6 +379,13 @@ static int upstream_bridge_distance(struct pci_dev *a,
> dist_a++;
> }
>
> + /* Allow the connection if both devices are on a whitelisted root
> + * complex, but add an arbitary large value to the distance.
> + */
> + if (root_complex_whitelist(provider) &&
> + root_complex_whitelist(client))
> + return 0x1000 + dist_a + dist_b;
> +
> return -1;
>
> check_b_path_acs:
> --
> 2.17.1
>
