[PATCH v4 4/7] PCI/ATS: Add PRI support for PCIe VF devices

[sathyanarayanan . kuppuswamy]

From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>

When IOMMU tries to enable Page Request Interface (PRI) for VF device
in iommu_enable_dev_iotlb(), it always fails because PRI support for
PCIe VF device is currently broken. Current implementation expects
the given PCIe device (PF & VF) to implement PRI capability before
enabling the PRI support. But this assumption is incorrect. As per PCIe
spec r4.0, sec 9.3.7.11, all VFs associated with PF can only use the
PRI of the PF and not implement it. Hence we need to create exception
for handling the PRI support for PCIe VF device.

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

1. Use proper locking before accessing/modifying PF resources in VF
   PRI enable/disable call.
2. Use reference count logic to track the usage of PRI resource.
3. Disable PRI only if the PRI reference count (pri_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   | 143 ++++++++++++++++++++++++++++++++++----------
 include/linux/pci.h |   2 +
 2 files changed, 112 insertions(+), 33 deletions(-)

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index b5ce40c54e0b..2066c819022d 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -31,6 +31,8 @@ static void pci_pri_init(struct pci_dev *pdev)
 	if (pdev->is_virtfn)
 		return;
 
+	mutex_init(&pdev->pri_lock);
+
 	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
 	if (!pos)
 		return;
@@ -260,29 +262,57 @@ int pci_enable_pri(struct pci_dev *pdev, u32 reqs)
 {
 	u16 control, status;
 	u32 max_requests;
+	int ret = 0;
+	struct pci_dev *pf = pci_physfn(pdev);
 
-	if (WARN_ON(pdev->pri_enabled))
-		return -EBUSY;
+	mutex_lock(&pf->pri_lock);
 
-	if (!pdev->pri_cap)
-		return -EINVAL;
+	if (WARN_ON(pdev->pri_enabled)) {
+		ret = -EBUSY;
+		goto pri_unlock;
+	}
 
-	pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_STATUS, &status);
-	if (!(status & PCI_PRI_STATUS_STOPPED))
-		return -EBUSY;
+	if (!pf->pri_cap) {
+		ret = -EINVAL;
+		goto pri_unlock;
+	}
+
+	if (pdev->is_virtfn && pf->pri_enabled)
+		goto update_status;
+
+	/*
+	 * Before updating PRI registers, make sure there is no
+	 * outstanding PRI requests.
+	 */
+	pci_read_config_word(pf, pf->pri_cap + PCI_PRI_STATUS, &status);
+	if (!(status & PCI_PRI_STATUS_STOPPED)) {
+		ret = -EBUSY;
+		goto pri_unlock;
+	}
 
-	pci_read_config_dword(pdev, pdev->pri_cap + PCI_PRI_MAX_REQ,
-			      &max_requests);
+	pci_read_config_dword(pf, pf->pri_cap + PCI_PRI_MAX_REQ, &max_requests);
 	reqs = min(max_requests, reqs);
-	pdev->pri_reqs_alloc = reqs;
-	pci_write_config_dword(pdev, pdev->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
+	pf->pri_reqs_alloc = reqs;
+	pci_write_config_dword(pf, pf->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
 
 	control = PCI_PRI_CTRL_ENABLE;
-	pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
+	pci_write_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, control);
 
-	pdev->pri_enabled = 1;
+	/*
+	 * If PRI is not already enabled in PF, increment the PF
+	 * pri_ref_cnt to track the usage of PRI interface.
+	 */
+	if (pdev->is_virtfn && !pf->pri_enabled) {
+		atomic_inc(&pf->pri_ref_cnt);
+		pf->pri_enabled = 1;
+	}
 
-	return 0;
+update_status:
+	atomic_inc(&pf->pri_ref_cnt);
+	pdev->pri_enabled = 1;
+pri_unlock:
+	mutex_unlock(&pf->pri_lock);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(pci_enable_pri);
 
@@ -295,18 +325,30 @@ EXPORT_SYMBOL_GPL(pci_enable_pri);
 void pci_disable_pri(struct pci_dev *pdev)
 {
 	u16 control;
+	struct pci_dev *pf = pci_physfn(pdev);
 
-	if (WARN_ON(!pdev->pri_enabled))
-		return;
+	mutex_lock(&pf->pri_lock);
 
-	if (!pdev->pri_cap)
-		return;
+	if (WARN_ON(!pdev->pri_enabled) || !pf->pri_cap)
+		goto pri_unlock;
+
+	atomic_dec(&pf->pri_ref_cnt);
 
-	pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, &control);
+	/*
+	 * If pri_ref_cnt is not zero, then don't modify hardware
+	 * registers.
+	 */
+	if (atomic_read(&pf->pri_ref_cnt))
+		goto done;
+
+	pci_read_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, &control);
 	control &= ~PCI_PRI_CTRL_ENABLE;
-	pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
+	pci_write_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, control);
 
+done:
 	pdev->pri_enabled = 0;
+pri_unlock:
+	mutex_unlock(&pf->pri_lock);
 }
 EXPORT_SYMBOL_GPL(pci_disable_pri);
 
@@ -316,17 +358,31 @@ EXPORT_SYMBOL_GPL(pci_disable_pri);
  */
 void pci_restore_pri_state(struct pci_dev *pdev)
 {
-	u16 control = PCI_PRI_CTRL_ENABLE;
-	u32 reqs = pdev->pri_reqs_alloc;
+	u16 control;
+	u32 reqs;
+	struct pci_dev *pf = pci_physfn(pdev);
 
 	if (!pdev->pri_enabled)
 		return;
 
-	if (!pdev->pri_cap)
+	if (!pf->pri_cap)
 		return;
 
-	pci_write_config_dword(pdev, pdev->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
-	pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
+	mutex_lock(&pf->pri_lock);
+
+	/* If PRI is already enabled by other VF's or PF, return */
+	pci_read_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, &control);
+	if (control & PCI_PRI_CTRL_ENABLE)
+		goto pri_unlock;
+
+	reqs = pf->pri_reqs_alloc;
+	control = PCI_PRI_CTRL_ENABLE;
+
+	pci_write_config_dword(pf, pf->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
+	pci_write_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, control);
+
+pri_unlock:
+	mutex_unlock(&pf->pri_lock);
 }
 EXPORT_SYMBOL_GPL(pci_restore_pri_state);
 
@@ -339,18 +395,32 @@ EXPORT_SYMBOL_GPL(pci_restore_pri_state);
  */
 int pci_reset_pri(struct pci_dev *pdev)
 {
+	struct pci_dev *pf = pci_physfn(pdev);
 	u16 control;
+	int ret = 0;
 
-	if (WARN_ON(pdev->pri_enabled))
-		return -EBUSY;
+	mutex_lock(&pf->pri_lock);
 
-	if (!pdev->pri_cap)
-		return -EINVAL;
+	if (WARN_ON(pdev->pri_enabled)) {
+		ret = -EBUSY;
+		goto done;
+	}
+
+	if (!pf->pri_cap) {
+		ret = -EINVAL;
+		goto done;
+	}
+
+	/* If PRI is already enabled by other VF's or PF, return 0 */
+	if (pf->pri_enabled)
+		goto done;
 
 	control = PCI_PRI_CTRL_RESET;
-	pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
 
-	return 0;
+	pci_write_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, control);
+done:
+	mutex_unlock(&pf->pri_lock);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(pci_reset_pri);
 #endif /* CONFIG_PCI_PRI */
@@ -480,11 +550,18 @@ EXPORT_SYMBOL_GPL(pci_pasid_features);
 int pci_prg_resp_pasid_required(struct pci_dev *pdev)
 {
 	u16 status;
+	struct pci_dev *pf = pci_physfn(pdev);
+
+	mutex_lock(&pf->pri_lock);
 
-	if (!pdev->pri_cap)
+	if (!pf->pri_cap) {
+		mutex_unlock(&pf->pri_lock);
 		return 0;
+	}
+
+	pci_read_config_word(pf, pf->pri_cap + PCI_PRI_STATUS, &status);
 
-	pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_STATUS, &status);
+	mutex_unlock(&pf->pri_lock);
 
 	if (status & PCI_PRI_STATUS_PASID)
 		return 1;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index b4010276dff6..d0075413b63f 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -452,8 +452,10 @@ struct pci_dev {
 	atomic_t	ats_ref_cnt;	/* Number of VFs with ATS enabled */
 #endif
 #ifdef CONFIG_PCI_PRI
+	struct mutex	pri_lock;	/* PRI enable lock */
 	u16		pri_cap;	/* PRI Capability offset */
 	u32		pri_reqs_alloc; /* Number of PRI requests allocated */
+	atomic_t	pri_ref_cnt;	/* Number of PF/VF PRI users */
 #endif
 #ifdef CONFIG_PCI_PASID
 	u16		pasid_cap;	/* PASID Capability offset */
-- 
2.21.0