[PATCH v1 2/3] vfio-pci/zdev: Add VFIO FMB device feature

Omar Elghoul
2026-05-01T19:27:10Z

Set up a new VFIO feature for zPCI devices to share the latest FMB snapshot
with userspace. This feature supports the same 4 FMB formats (0 through 3)
that are already supported by the kernel.

With VFIO_DEVICE_FEATURE_GET, allow the user driver to read the latest FMB
snapshot as well as query whether the FMB is currently enabled on the
function, itself indicating whether the FMB snapshot is valid. On the other
hand, with VFIO_DEVICE_FEATURE_SET, the userspace driver can enable or
disable the FMB.

Signed-off-by: Omar Elghoul <oelghoul@linux.ibm.com>
---
drivers/vfio/pci/vfio_pci_core.c | 2 +
drivers/vfio/pci/vfio_pci_priv.h | 9 ++++
drivers/vfio/pci/vfio_pci_zdev.c | 77 ++++++++++++++++++++++++++++++++
include/uapi/linux/vfio.h | 43 ++++++++++++++++++
4 files changed, 131 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 3f8d093aacf8..63e80b6fa0dc 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1534,6 +1534,8 @@ int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
return vfio_pci_core_feature_token(vdev, flags, arg, argsz);
case VFIO_DEVICE_FEATURE_DMA_BUF:
return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz);
+ case VFIO_DEVICE_FEATURE_ZPCI_FMB:
+ return vfio_pci_zdev_feature_fmb(vdev, flags, arg, argsz);
default:
return -ENOTTY;
}
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index fca9d0dfac90..208e05942b48 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -93,6 +93,8 @@ int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
struct vfio_info_cap *caps);
int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev);
void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev);
+int vfio_pci_zdev_feature_fmb(struct vfio_pci_core_device *vdev, u32 flags,
+ void __user *arg, size_t argsz);
#else
static inline int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
struct vfio_info_cap *caps)
@@ -107,6 +109,13 @@ static inline int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)

static inline void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
{}
+
+static inline int vfio_pci_zdev_feature_fmb(struct vfio_pci_core_device *vdev,
+ u32 flags, void __user *arg,
+ size_t argsz)
+{
+ return -ENOTTY;
+}
#endif

static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
index 0990fdb146b7..1e9efe2bee69 100644
--- a/drivers/vfio/pci/vfio_pci_zdev.c
+++ b/drivers/vfio/pci/vfio_pci_zdev.c
@@ -167,3 +167,80 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
if (zpci_kvm_hook.kvm_unregister)
zpci_kvm_hook.kvm_unregister(zdev);
}
+
+int vfio_pci_zdev_feature_fmb(struct vfio_pci_core_device *vdev, u32 flags,
+ void __user *arg, size_t argsz)
+{
+ struct zpci_dev *zdev;
+ struct vfio_device_feature_zpci_fmb fmb = {0};
+ u32 ops = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_SET;
+ int ret;
+
+ ret = vfio_check_feature(flags, argsz, ops, sizeof(fmb));
+ if (ret != 1)
+ return ret;
+
+ zdev = to_zpci(vdev->pdev);
+ if (!zdev)
+ return -ENODEV;
+
+ mutex_lock(&zdev->fmb_lock);
+ if (flags & VFIO_DEVICE_FEATURE_SET) {
+ if (copy_from_user(&fmb, arg, sizeof(fmb))) {
+ ret = -EFAULT;
+ goto release_lock;
+ }
+
+ if (fmb.flags & VFIO_DEVICE_FEATURE_ZPCI_FMB_FLAGS_ENABLED)
+ ret = zpci_fmb_reenable_device(zdev);
+ else
+ ret = zpci_fmb_disable_device(zdev);
+ goto release_lock;
+ }
+
+ ret = 0;
+ if (zdev->fmb) {
+ fmb.flags |= VFIO_DEVICE_FEATURE_ZPCI_FMB_FLAGS_ENABLED;
+ } else {
+ fmb.flags &= ~VFIO_DEVICE_FEATURE_ZPCI_FMB_FLAGS_ENABLED;
+ goto release_lock;
+ }
+
+ fmb.format = zdev->fmb->format;
+ fmb.fmt_ind = zdev->fmb->fmt_ind;
+ fmb.samples = zdev->fmb->samples;
+ fmb.last_update = zdev->fmb->last_update;
+ fmb.ld_ops = zdev->fmb->ld_ops;
+ fmb.st_ops = zdev->fmb->st_ops;
+ fmb.stb_ops = zdev->fmb->stb_ops;
+ fmb.rpcit_ops = zdev->fmb->rpcit_ops;
+
+ switch (zdev->fmb->format) {
+ case 0:
+ if (zdev->fmb->fmt_ind & ZPCI_FMB_DMA_COUNTER_VALID) {
+ fmb.fmt0.dma_rbytes = zdev->fmb->fmt0.dma_rbytes;
+ fmb.fmt0.dma_wbytes = zdev->fmb->fmt0.dma_wbytes;
+ }
+ break;
+ case 1:
+ fmb.fmt1.rx_bytes = zdev->fmb->fmt1.rx_bytes;
+ fmb.fmt1.rx_packets = zdev->fmb->fmt1.rx_packets;
+ fmb.fmt1.tx_bytes = zdev->fmb->fmt1.tx_bytes;
+ fmb.fmt1.tx_packets = zdev->fmb->fmt1.tx_packets;
+ break;
+ case 2:
+ fmb.fmt2.consumed_work_units = zdev->fmb->fmt2.consumed_work_units;
+ fmb.fmt2.max_work_units = zdev->fmb->fmt2.max_work_units;
+ break;
+ case 3:
+ fmb.fmt3.tx_bytes = zdev->fmb->fmt3.tx_bytes;
+ break;
+ }
+
+ if (copy_to_user(arg, &fmb, sizeof(fmb)))
+ ret = -EFAULT;
+
+release_lock:
+ mutex_unlock(&zdev->fmb_lock);
+ return ret;
+}
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 5de618a3a5ee..6cbc34ff063e 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1534,6 +1534,49 @@ struct vfio_device_feature_dma_buf {
*/
#define VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2 12

+/**
+ * Upon VFIO_DEVICE_FEATURE_GET, provide FMB passthrough for VFIO zPCI devices.
+ *
+ * Upon VFIO_DEVICE_FEATURE_SET, only the flags field is read while the
+ * remainder of the structure is ignored. This allows the driver to enable or
+ * disable the FMB while also leaving reserved bits for future flag expansion.
+ * All reserved fields should be zero for future compatibility.
+ */
+#define VFIO_DEVICE_FEATURE_ZPCI_FMB 13
+#define VFIO_DEVICE_FEATURE_ZPCI_FMB_FLAGS_ENABLED 0x1
+
+struct vfio_device_feature_zpci_fmb {
+ __u64 flags;
+ __u32 format: 8;
+ __u32 fmt_ind: 24;
+ __u32 samples;
+ __u64 last_update;
+ __u64 ld_ops;
+ __u64 st_ops;
+ __u64 stb_ops;
+ __u64 rpcit_ops;
+ union {
+ struct {
+ __u64 dma_rbytes;
+ __u64 dma_wbytes;
+ } fmt0;
+ struct {
+ __u64 rx_bytes;
+ __u64 rx_packets;
+ __u64 tx_bytes;
+ __u64 tx_packets;
+ } fmt1;
+ struct {
+ __u64 consumed_work_units;
+ __u64 max_work_units;
+ } fmt2;
+ struct {
+ __u64 tx_bytes;
+ } fmt3;
+ };
+ __u64 reserved[16];
+};
+
/* -------- API for Type1 VFIO IOMMU -------- */

/**
--
2.52.0