[PATCH v5 5/7] PCI/ATS: Add PASID support for PCIe VF devices

[sathyanarayanan . kuppuswamy]

From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>

When IOMMU tries to enable PASID for VF device in
iommu_enable_dev_iotlb(), it always fails because PASID support for PCIe
VF device is currently broken in PCIE driver. Current implementation
expects the given PCIe device (PF & VF) to implement PASID capability
before enabling the PASID support. But this assumption is incorrect. As
per PCIe spec r4.0, sec 9.3.7.14, all VFs associated with PF can only
use the PASID of the PF and not implement it.

Also, since PASID is a shared resource between PF/VF, following rules
should apply.

1. Use proper locking before accessing/modifying PF resources in VF
   PASID enable/disable call.
2. Use reference count logic to track the usage of PASID resource.
3. Disable PASID only if the PASID reference count (pasid_ref_cnt) is zero.

Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: Keith Busch <keith.busch@xxxxxxxxx>
Suggested-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
---
 drivers/pci/ats.c   | 113 ++++++++++++++++++++++++++++++++++----------
 include/linux/pci.h |   2 +
 2 files changed, 90 insertions(+), 25 deletions(-)

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index 079dc5444444..9384afd7d00e 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -402,6 +402,8 @@ void pci_pasid_init(struct pci_dev *pdev)
 	if (pdev->is_virtfn)
 		return;
 
+	mutex_init(&pdev->pasid_lock);
+
 	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
 	if (!pos)
 		return;
@@ -436,32 +438,57 @@ void pci_pasid_init(struct pci_dev *pdev)
 int pci_enable_pasid(struct pci_dev *pdev, int features)
 {
 	u16 control, supported;
+	int ret = 0;
+	struct pci_dev *pf = pci_physfn(pdev);
 
-	if (WARN_ON(pdev->pasid_enabled))
-		return -EBUSY;
+	mutex_lock(&pf->pasid_lock);
 
-	if (!pdev->eetlp_prefix_path)
-		return -EINVAL;
+	if (WARN_ON(pdev->pasid_enabled)) {
+		ret = -EBUSY;
+		goto pasid_unlock;
+	}
 
-	if (!pdev->pasid_cap)
-		return -EINVAL;
+	if (!pdev->eetlp_prefix_path) {
+		ret = -EINVAL;
+		goto pasid_unlock;
+	}
 
-	pci_read_config_word(pdev, pdev->pasid_cap + PCI_PASID_CAP,
-			     &supported);
+	if (!pf->pasid_cap) {
+		ret = -EINVAL;
+		goto pasid_unlock;
+	}
+
+	if (pdev->is_virtfn && pf->pasid_enabled)
+		goto update_status;
+
+	pci_read_config_word(pf, pf->pasid_cap + PCI_PASID_CAP, &supported);
 	supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;
 
 	/* User wants to enable anything unsupported? */
-	if ((supported & features) != features)
-		return -EINVAL;
+	if ((supported & features) != features) {
+		ret = -EINVAL;
+		goto pasid_unlock;
+	}
 
 	control = PCI_PASID_CTRL_ENABLE | features;
-	pdev->pasid_features = features;
-
+	pf->pasid_features = features;
 	pci_write_config_word(pdev, pdev->pasid_cap + PCI_PASID_CTRL, control);
 
-	pdev->pasid_enabled = 1;
+	/*
+	 * If PASID is not already enabled in PF, increment pasid_ref_cnt
+	 * to count PF PASID usage.
+	 */
+	if (pdev->is_virtfn && !pf->pasid_enabled) {
+		atomic_inc(&pf->pasid_ref_cnt);
+		pf->pasid_enabled = 1;
+	}
 
-	return 0;
+update_status:
+	atomic_inc(&pf->pasid_ref_cnt);
+	pdev->pasid_enabled = 1;
+pasid_unlock:
+	mutex_unlock(&pf->pasid_lock);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(pci_enable_pasid);
 
@@ -472,16 +499,29 @@ EXPORT_SYMBOL_GPL(pci_enable_pasid);
 void pci_disable_pasid(struct pci_dev *pdev)
 {
 	u16 control = 0;
+	struct pci_dev *pf = pci_physfn(pdev);
+
+	mutex_lock(&pf->pasid_lock);
 
 	if (WARN_ON(!pdev->pasid_enabled))
-		return;
+		goto pasid_unlock;
 
-	if (!pdev->pasid_cap)
-		return;
+	if (!pf->pasid_cap)
+		goto pasid_unlock;
 
-	pci_write_config_word(pdev, pdev->pasid_cap + PCI_PASID_CTRL, control);
+	atomic_dec(&pf->pasid_ref_cnt);
 
+	if (atomic_read(&pf->pasid_ref_cnt))
+		goto done;
+
+	/* Disable PASID only if pasid_ref_cnt is zero */
+	pci_write_config_word(pf, pf->pasid_cap + PCI_PASID_CTRL, control);
+
+done:
 	pdev->pasid_enabled = 0;
+pasid_unlock:
+	mutex_unlock(&pf->pasid_lock);
+
 }
 EXPORT_SYMBOL_GPL(pci_disable_pasid);
 
@@ -492,15 +532,25 @@ EXPORT_SYMBOL_GPL(pci_disable_pasid);
 void pci_restore_pasid_state(struct pci_dev *pdev)
 {
 	u16 control;
+	struct pci_dev *pf = pci_physfn(pdev);
 
 	if (!pdev->pasid_enabled)
 		return;
 
-	if (!pdev->pasid_cap)
+	if (!pf->pasid_cap)
 		return;
 
+	mutex_lock(&pf->pasid_lock);
+
+	pci_read_config_word(pf, pf->pasid_cap + PCI_PASID_CTRL, &control);
+	if (control & PCI_PASID_CTRL_ENABLE)
+		goto pasid_unlock;
+
 	control = PCI_PASID_CTRL_ENABLE | pdev->pasid_features;
-	pci_write_config_word(pdev, pdev->pasid_cap + PCI_PASID_CTRL, control);
+	pci_write_config_word(pf, pf->pasid_cap + PCI_PASID_CTRL, control);
+
+pasid_unlock:
+	mutex_unlock(&pf->pasid_lock);
 }
 EXPORT_SYMBOL_GPL(pci_restore_pasid_state);
 
@@ -517,15 +567,22 @@ EXPORT_SYMBOL_GPL(pci_restore_pasid_state);
 int pci_pasid_features(struct pci_dev *pdev)
 {
 	u16 supported;
+	struct pci_dev *pf = pci_physfn(pdev);
+
+	mutex_lock(&pf->pasid_lock);
 
-	if (!pdev->pasid_cap)
+	if (!pf->pasid_cap) {
+		mutex_unlock(&pf->pasid_lock);
 		return -EINVAL;
+	}
 
-	pci_read_config_word(pdev, pdev->pasid_cap + PCI_PASID_CAP,
+	pci_read_config_word(pf, pf->pasid_cap + PCI_PASID_CAP,
 			     &supported);
 
 	supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;
 
+	mutex_unlock(&pf->pasid_lock);
+
 	return supported;
 }
 EXPORT_SYMBOL_GPL(pci_pasid_features);
@@ -579,15 +636,21 @@ EXPORT_SYMBOL_GPL(pci_prg_resp_pasid_required);
 int pci_max_pasids(struct pci_dev *pdev)
 {
 	u16 supported;
+	struct pci_dev *pf = pci_physfn(pdev);
+
+	mutex_lock(&pf->pasid_lock);
 
-	if (!pdev->pasid_cap)
+	if (!pf->pasid_cap) {
+		mutex_unlock(&pf->pasid_lock);
 		return -EINVAL;
+	}
 
-	pci_read_config_word(pdev, pdev->pasid_cap + PCI_PASID_CAP,
-			     &supported);
+	pci_read_config_word(pf, pf->pasid_cap + PCI_PASID_CAP, &supported);
 
 	supported = (supported & PASID_NUMBER_MASK) >> PASID_NUMBER_SHIFT;
 
+	mutex_unlock(&pf->pasid_lock);
+
 	return (1 << supported);
 }
 EXPORT_SYMBOL_GPL(pci_max_pasids);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 3c9c4c82be27..4bfcca045afd 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -461,8 +461,10 @@ struct pci_dev {
 	atomic_t	pri_ref_cnt;	/* Number of PF/VF PRI users */
 #endif
 #ifdef CONFIG_PCI_PASID
+	struct mutex	pasid_lock;	/* PASID enable lock */
 	u16		pasid_cap;	/* PASID Capability offset */
 	u16		pasid_features;
+	atomic_t	pasid_ref_cnt;	/* Number of VFs with PASID enabled */
 #endif
 #ifdef CONFIG_PCI_P2PDMA
 	struct pci_p2pdma *p2pdma;
-- 
2.21.0