Allocate the FMB once upon first enable and keep it for the lifetime of
the zdev instead of freeing it on every disable. Track the enablement
state in the new statistics_on bool, since a non-null FMB no longer
implies that measurement is enabled. Defer freeing the buffer until
device teardown in zpci_release_device().

Drop the alignment warning after allocating the FMB buffer due to it
already being guaranteed by the kmem_cache.

Audit the only consumer of the FMB (pci_perf_show) and update its
liveness check to be aware of this change.

Signed-off-by: Omar Elghoul <oelghoul@linux.ibm.com>
---
 arch/s390/include/asm/pci.h |  1 +
 arch/s390/pci/pci.c         | 41 ++++++++++++++++++++++---------------
 arch/s390/pci/pci_debug.c   |  2 +-
 3 files changed, 27 insertions(+), 17 deletions(-)

diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
index 88a125b92bdd..f4fea1c34746 100644
--- a/arch/s390/include/asm/pci.h
+++ b/arch/s390/include/asm/pci.h
@@ -208,6 +208,7 @@ struct zpci_dev {
 	struct zpci_fmb *fmb;
 	u16		fmb_update;	/* update interval */
 	u16		fmb_length;
+	bool		statistics_on;
 
 	u8		version;
 	enum pci_bus_speed max_bus_speed;
diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index c055a9ad0972..2a7e1ca0fa12 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -175,13 +175,17 @@ int zpci_fmb_enable_device(struct zpci_dev *zdev)
 
 	lockdep_assert_held(&zdev->fmb_lock);
 
-	if (zdev->fmb || sizeof(*zdev->fmb) < zdev->fmb_length)
+	if (zdev->statistics_on || sizeof(*zdev->fmb) < zdev->fmb_length)
 		return -EINVAL;
 
-	zdev->fmb = kmem_cache_zalloc(zdev_fmb_cache, GFP_KERNEL);
-	if (!zdev->fmb)
-		return -ENOMEM;
-	WARN_ON((u64) zdev->fmb & 0xf);
+	if (!zdev->fmb) {
+		zdev->fmb = kmem_cache_zalloc(zdev_fmb_cache, GFP_KERNEL);
+		if (!zdev->fmb)
+			return -ENOMEM;
+	} else {
+		/* reuse the same FMB buffer for as long as the zdev lives */
+		memset(zdev->fmb, 0, sizeof(*zdev->fmb));
+	}
 
 	/* reset software counters */
 	spin_lock_irqsave(&zdev->dom_lock, flags);
@@ -199,11 +203,11 @@ int zpci_fmb_enable_device(struct zpci_dev *zdev)
 	fib.fmb_addr = virt_to_phys(zdev->fmb);
 	fib.gd = zdev->gisa;
 	cc = zpci_mod_fc(req, &fib, &status);
-	if (cc) {
-		kmem_cache_free(zdev_fmb_cache, zdev->fmb);
-		zdev->fmb = NULL;
-	}
-	return cc ? -EIO : 0;
+	if (cc)
+		return -EIO;
+
+	zdev->statistics_on = true;
+	return 0;
 }
 
 /* Modify PCI: Disable PCI function measurement */
@@ -215,7 +219,7 @@ int zpci_fmb_disable_device(struct zpci_dev *zdev)
 
 	lockdep_assert_held(&zdev->fmb_lock);
 
-	if (!zdev->fmb)
+	if (!zdev->statistics_on)
 		return -EINVAL;
 
 	fib.gd = zdev->gisa;
@@ -224,12 +228,11 @@ int zpci_fmb_disable_device(struct zpci_dev *zdev)
 	cc = zpci_mod_fc(req, &fib, &status);
 	if (cc == 3) /* Function already gone. */
 		cc = 0;
+	if (cc)
+		return -EIO;
 
-	if (!cc) {
-		kmem_cache_free(zdev_fmb_cache, zdev->fmb);
-		zdev->fmb = NULL;
-	}
-	return cc ? -EIO : 0;
+	zdev->statistics_on = false;
+	return 0;
 }
 
 static int zpci_cfg_load(struct zpci_dev *zdev, int offset, u32 *val, u8 len)
@@ -1003,6 +1006,12 @@ void zpci_release_device(struct kref *kref)
 	if (zdev->has_resources)
 		zpci_cleanup_bus_resources(zdev);
 
+	if (zdev->fmb) {
+		zdev->statistics_on = false;
+		kmem_cache_free(zdev_fmb_cache, zdev->fmb);
+		zdev->fmb = NULL;
+	}
+
 	zpci_bus_device_unregister(zdev);
 	zpci_destroy_iommu(zdev);
 	zpci_dbg(3, "rem fid:%x\n", zdev->fid);
diff --git a/arch/s390/pci/pci_debug.c b/arch/s390/pci/pci_debug.c
index c7ed7bf254b5..419c6a9200a2 100644
--- a/arch/s390/pci/pci_debug.c
+++ b/arch/s390/pci/pci_debug.c
@@ -97,7 +97,7 @@ static int pci_perf_show(struct seq_file *m, void *v)
 		return 0;
 
 	mutex_lock(&zdev->fmb_lock);
-	if (!zdev->fmb) {
+	if (!zdev->statistics_on || !zdev->fmb) {
 		mutex_unlock(&zdev->fmb_lock);
 		seq_puts(m, "FMB statistics disabled\n");
 		return 0;
-- 
2.56.0