[PATCH v10 3/5] s390/pci: Improve function measurement state management

[Omar Elghoul <oelghoul@linux.ibm.com>]

When a zPCI function is disabled and re-enabled, the firmware implicitly
disables function measurement while the kernel still believes it is
enabled, leading to a disconnect between the user-visible state and the
actual device state.

Make statistics_on represent the requested state instead. Introduce the
functions zpci_fmb_request_on() and off(), which call zpci_fmb_enable()
or disable() to perform the actual firmware change. This decouples the
enablement or disablement from managing the user's desired state.

Preserve the state in pcibios_enable_device(), pcibios_disable_device(),
and zpci_reenable_device(), so measurement is restored automatically
after a re-enable. New devices start with measurement on by default,
unchanged from before.

Signed-off-by: Omar Elghoul <oelghoul@linux.ibm.com>
---
 arch/s390/include/asm/pci.h |  8 +++--
 arch/s390/pci/pci.c         | 63 ++++++++++++++++++++++++++++++-------
 arch/s390/pci/pci_debug.c   |  4 +--
 3 files changed, 58 insertions(+), 17 deletions(-)

diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
index f4fea1c34746..dd7a17955362 100644
--- a/arch/s390/include/asm/pci.h
+++ b/arch/s390/include/asm/pci.h
@@ -208,7 +208,7 @@ struct zpci_dev {
 	struct zpci_fmb *fmb;
 	u16		fmb_update;	/* update interval */
 	u16		fmb_length;
-	bool		statistics_on;
+	bool		statistics_on;	/* desired FMB enablement */
 
 	u8		version;
 	enum pci_bus_speed max_bus_speed;
@@ -350,8 +350,10 @@ int zpci_create_parent_msi_domain(struct zpci_bus *zbus);
 void zpci_remove_parent_msi_domain(struct zpci_bus *zbus);
 
 /* FMB */
-int zpci_fmb_enable_device(struct zpci_dev *);
-int zpci_fmb_disable_device(struct zpci_dev *);
+int zpci_fmb_request_on(struct zpci_dev *zdev);
+int zpci_fmb_request_off(struct zpci_dev *zdev);
+int zpci_fmb_enable(struct zpci_dev *zdev);
+int zpci_fmb_disable(struct zpci_dev *zdev);
 
 /* Debug */
 int zpci_debug_init(void);
diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 2a7e1ca0fa12..98a4e938865a 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -165,7 +165,37 @@ int zpci_unregister_ioat(struct zpci_dev *zdev, u8 dmaas)
 }
 
 /* Modify PCI: Set PCI function measurement parameters */
-int zpci_fmb_enable_device(struct zpci_dev *zdev)
+int zpci_fmb_request_on(struct zpci_dev *zdev)
+{
+	lockdep_assert_held(&zdev->fmb_lock);
+
+	if (zdev->statistics_on && zdev->fmb)
+		return -EINVAL;
+
+	/*
+	 * Record the user's intent first. If the enable fails, the flag stays set
+	 * so we can retry enabling the FMB upon the next device (re-)enable. The
+	 * consumer can detect that a measurement sample was never written if the
+	 * timestamp is still zero, or if the FMB pointer is null.
+	 */
+	zdev->statistics_on = true;
+	return zpci_fmb_enable(zdev);
+}
+
+/* Modify PCI: Disable PCI function measurement */
+int zpci_fmb_request_off(struct zpci_dev *zdev)
+{
+	lockdep_assert_held(&zdev->fmb_lock);
+
+	if (!zdev->statistics_on)
+		return -EINVAL;
+
+	zdev->statistics_on = false;
+	return zpci_fmb_disable(zdev);
+}
+EXPORT_SYMBOL_GPL(zpci_fmb_request_off);
+
+int zpci_fmb_enable(struct zpci_dev *zdev)
 {
 	u64 req = ZPCI_CREATE_REQ(zdev->fh, 0, ZPCI_MOD_FC_SET_MEASURE);
 	struct zpci_iommu_ctrs *ctrs;
@@ -175,7 +205,7 @@ int zpci_fmb_enable_device(struct zpci_dev *zdev)
 
 	lockdep_assert_held(&zdev->fmb_lock);
 
-	if (zdev->statistics_on || sizeof(*zdev->fmb) < zdev->fmb_length)
+	if (sizeof(*zdev->fmb) < zdev->fmb_length)
 		return -EINVAL;
 
 	if (!zdev->fmb) {
@@ -206,12 +236,11 @@ int zpci_fmb_enable_device(struct zpci_dev *zdev)
 	if (cc)
 		return -EIO;
 
-	zdev->statistics_on = true;
 	return 0;
 }
+EXPORT_SYMBOL_GPL(zpci_fmb_enable);
 
-/* Modify PCI: Disable PCI function measurement */
-int zpci_fmb_disable_device(struct zpci_dev *zdev)
+int zpci_fmb_disable(struct zpci_dev *zdev)
 {
 	u64 req = ZPCI_CREATE_REQ(zdev->fh, 0, ZPCI_MOD_FC_SET_MEASURE);
 	struct zpci_fib fib = {0};
@@ -219,9 +248,6 @@ int zpci_fmb_disable_device(struct zpci_dev *zdev)
 
 	lockdep_assert_held(&zdev->fmb_lock);
 
-	if (!zdev->statistics_on)
-		return -EINVAL;
-
 	fib.gd = zdev->gisa;
 
 	/* Function measurement is disabled if fmb address is zero */
@@ -231,7 +257,6 @@ int zpci_fmb_disable_device(struct zpci_dev *zdev)
 	if (cc)
 		return -EIO;
 
-	zdev->statistics_on = false;
 	return 0;
 }
 
@@ -647,7 +672,8 @@ int pcibios_enable_device(struct pci_dev *pdev, int mask)
 
 	zpci_debug_init_device(zdev, dev_name(&pdev->dev));
 	mutex_lock(&zdev->fmb_lock);
-	zpci_fmb_enable_device(zdev);
+	if (zdev->statistics_on)
+		zpci_fmb_enable(zdev);
 	mutex_unlock(&zdev->fmb_lock);
 
 	return pci_enable_resources(pdev, mask);
@@ -658,7 +684,8 @@ void pcibios_disable_device(struct pci_dev *pdev)
 	struct zpci_dev *zdev = to_zpci(pdev);
 
 	mutex_lock(&zdev->fmb_lock);
-	zpci_fmb_disable_device(zdev);
+	if (zdev->statistics_on)
+		zpci_fmb_disable(zdev);
 	mutex_unlock(&zdev->fmb_lock);
 	zpci_debug_exit_device(zdev);
 }
@@ -740,8 +767,14 @@ int zpci_reenable_device(struct zpci_dev *zdev)
 	}
 
 	rc = zpci_iommu_register_ioat(zdev, &status);
-	if (rc)
+	if (rc) {
 		zpci_disable_device(zdev);
+		return rc;
+	}
+
+	guard(mutex)(&zdev->fmb_lock);
+	if (zdev->statistics_on)
+		zpci_fmb_enable(zdev);
 
 	return rc;
 }
@@ -850,6 +883,12 @@ struct zpci_dev *zpci_create_device(u32 fid, u32 fh, enum zpci_state state)
 		goto error;
 	zdev->state =  state;
 
+	/*
+	 * Measurement is on by default for new functions, this will be honored
+	 * by pcibios_enable_device().
+	 */
+	zdev->statistics_on = true;
+
 	mutex_init(&zdev->state_lock);
 	mutex_init(&zdev->fmb_lock);
 	mutex_init(&zdev->kzdev_lock);
diff --git a/arch/s390/pci/pci_debug.c b/arch/s390/pci/pci_debug.c
index 419c6a9200a2..e479763858cd 100644
--- a/arch/s390/pci/pci_debug.c
+++ b/arch/s390/pci/pci_debug.c
@@ -156,10 +156,10 @@ static ssize_t pci_perf_seq_write(struct file *file, const char __user *ubuf,
 	mutex_lock(&zdev->fmb_lock);
 	switch (val) {
 	case 0:
-		rc = zpci_fmb_disable_device(zdev);
+		rc = zpci_fmb_request_off(zdev);
 		break;
 	case 1:
-		rc = zpci_fmb_enable_device(zdev);
+		rc = zpci_fmb_request_on(zdev);
 		break;
 	}
 	mutex_unlock(&zdev->fmb_lock);
-- 
2.56.0