PCI/P2PDMA: Whitelist some Intel host bridges

Intel devices do not have good support for P2P requests that span different
host bridges as the transactions will cross the QPI/UPI bus and this does
not perform well.

Therefore, enable support for these devices only if the host bridges match.

Add Intel devices that have been tested and are known to work. There are
likely many others out there that will need to be tested and added.

Link: https://lore.kernel.org/r/20190730163545.4915-8-logang@deltatee.com
Link: https://lore.kernel.org/r/20190812173048.9186-8-logang@deltatee.comSigned-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

drivers/pci/p2pdma.c

@@ -269,9 +269,30 @@ static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
 	seq_buf_printf(buf, "%s;", pci_name(pdev));
 }
 
-static bool __host_bridge_whitelist(struct pci_host_bridge *host)
+static const struct pci_p2pdma_whitelist_entry {
+	unsigned short vendor;
+	unsigned short device;
+	enum {
+		REQ_SAME_HOST_BRIDGE	= 1 << 0,
+	} flags;
+} pci_p2pdma_whitelist[] = {
+	/* AMD ZEN */
+	{PCI_VENDOR_ID_AMD,	0x1450,	0},
+
+	/* Intel Xeon E5/Core i7 */
+	{PCI_VENDOR_ID_INTEL,	0x3c00, REQ_SAME_HOST_BRIDGE},
+	{PCI_VENDOR_ID_INTEL,	0x3c01, REQ_SAME_HOST_BRIDGE},
+	/* Intel Xeon E7 v3/Xeon E5 v3/Core i7 */
+	{PCI_VENDOR_ID_INTEL,	0x2f00, REQ_SAME_HOST_BRIDGE},
+	{PCI_VENDOR_ID_INTEL,	0x2f01, REQ_SAME_HOST_BRIDGE},
+	{}
+};
+
+static bool __host_bridge_whitelist(struct pci_host_bridge *host,
+				    bool same_host_bridge)
 {
 	struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
+	const struct pci_p2pdma_whitelist_entry *entry;
 	unsigned short vendor, device;
 
 	if (!root)
@@ -281,9 +302,14 @@ static bool __host_bridge_whitelist(struct pci_host_bridge *host)
 	device = root->device;
 	pci_dev_put(root);
 
-	/* AMD ZEN host bridges can do peer to peer */
-	if (vendor == PCI_VENDOR_ID_AMD && device == 0x1450)
+	for (entry = pci_p2pdma_whitelist; entry->vendor; entry++) {
+		if (vendor != entry->vendor || device != entry->device)
+			continue;
+		if (entry->flags & REQ_SAME_HOST_BRIDGE && !same_host_bridge)
+			return false;
+
 		return true;
+	}
 
 	return false;
 }
@@ -300,7 +326,11 @@ static bool host_bridge_whitelist(struct pci_dev *a, struct pci_dev *b)
 	if (iommu_present(a->dev.bus) || iommu_present(b->dev.bus))
 		return false;
 
-	if (__host_bridge_whitelist(host_a) && __host_bridge_whitelist(host_b))
+	if (host_a == host_b)
+		return __host_bridge_whitelist(host_a, true);
+
+	if (__host_bridge_whitelist(host_a, false) &&
+	    __host_bridge_whitelist(host_b, false))
 		return true;
 
 	return false;