[PATCH v10 3/5] s390/pci: Improve function measurement state management
From: Omar Elghoul
Date: Tue Oct 20 2026 - 17:26:55 EST
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@xxxxxxxxxxxxx>
---
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