[PATCH V8 6/8] PCI/P2PDMA: Add a 10-Bit Tag check in P2PDMA

[Dongdong Liu <liudongdong3@huawei.com>]

Add a 10-Bit Tag check in the P2PDMA code to ensure that a device with
10-Bit Tag Requester doesn't interact with a device that does not
support 10-Bit Tag Completer. Before that happens, the kernel should
emit a warning.

"echo 0 > /sys/bus/pci/devices/.../10bit_tag" to disable 10-Bit Tag
Requester for PF device.

"echo 0 > /sys/bus/pci/devices/.../sriov_vf_10bit_tag_ctl" to disable
10-Bit Tag Requester for VF device.

Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
---
 drivers/pci/p2pdma.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 50cdde3..2b9c2c9 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -19,6 +19,7 @@
 #include <linux/random.h>
 #include <linux/seq_buf.h>
 #include <linux/xarray.h>
+#include "pci.h"
 
 enum pci_p2pdma_map_type {
 	PCI_P2PDMA_MAP_UNKNOWN = 0,
@@ -410,6 +411,50 @@ static unsigned long map_types_idx(struct pci_dev *client)
 		(client->bus->number << 8) | client->devfn;
 }
 
+static bool pci_10bit_tags_unsupported(struct pci_dev *a,
+				       struct pci_dev *b,
+				       bool verbose)
+{
+	bool req;
+	bool comp;
+	u16 ctl;
+	const char *str = "10bit_tag";
+
+	if (a->is_virtfn) {
+#ifdef CONFIG_PCI_IOV
+		req = !!(a->physfn->sriov->ctrl &
+			 PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN);
+#endif
+	} else {
+		pcie_capability_read_word(a, PCI_EXP_DEVCTL2, &ctl);
+		req = !!(ctl & PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN);
+	}
+
+	comp = !!(b->pcie_devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_COMP);
+
+	/* 10-bit tags not enabled on requester */
+	if (!req)
+		return false;
+
+	 /* Completer can handle anything */
+	if (comp)
+		return false;
+
+	if (!verbose)
+		return true;
+
+	pci_warn(a, "cannot be used for peer-to-peer DMA as 10-Bit Tag Requester enable is set for this device, but peer device (%s) does not support the 10-Bit Tag Completer\n",
+		 pci_name(b));
+
+	if (a->is_virtfn)
+		str = "sriov_vf_10bit_tag_ctl";
+
+	pci_warn(a, "to disable 10-Bit Tag Requester for this device, echo 0 > /sys/bus/pci/devices/%s/%s\n",
+		 pci_name(a), str);
+
+	return true;
+}
+
 /*
  * Calculate the P2PDMA mapping type and distance between two PCI devices.
  *
@@ -532,6 +577,9 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
 		map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
 	}
 done:
+	if (pci_10bit_tags_unsupported(client, provider, verbose))
+		map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
+
 	rcu_read_lock();
 	p2pdma = rcu_dereference(provider->p2pdma);
 	if (p2pdma)
-- 
2.7.4