[PATCH v7 0/2] PCI: s390: Expose the UID as an arch specific PCI slot attribute

[PATCH v7 0/2] PCI: s390: Expose the UID as an arch specific PCI slot attribute

[Niklas Schnelle]

Hi all,

Add a mechanism for architecture specific attributes on
PCI slots in order to add the user-defined ID (UID) as an s390 specific
PCI slot attribute. First though improve some issues with the s390 specific
documentation of PCI sysfs attributes noticed during development. 

Also note, I considered adding the UID as a generic slot index attribute
analogous to the PCI device index attribute (SMBIOS index / s390 UID)
but decided against it as this seems rather s390 specific and having
it named UID makes things easier for users and aligns with the existing
separate uid device attribute.

Thanks,
Niklas

v6->v7:
- Incorporate doc suggestions from Randy Dunlap
- Add R-b, T-b and A-b
- Rebase on v7.0-rc7
- Link to v6: https://lore.kernel.org/r/20260402-uid_slot-v6-0-d5ea0a14ddb9@linux.ibm.com
v5->v6:
- Add documentation cleanup patch before adding new slot attribute
- Link to v5: https://lore.kernel.org/r/20260401-uid_slot-v5-1-e73036c74bf6@linux.ibm.com

Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
---

---
Niklas Schnelle (2):
      docs: s390/pci: Improve and update PCI documentation
      PCI: s390: Expose the UID as an arch specific PCI slot attribute

 Documentation/arch/s390/pci.rst | 151 +++++++++++++++++++++++++++-------------
 arch/s390/include/asm/pci.h     |   4 ++
 arch/s390/pci/pci_sysfs.c       |  20 ++++++
 drivers/pci/slot.c              |  13 +++-
 4 files changed, 140 insertions(+), 48 deletions(-)
---
base-commit: 591cd656a1bf5ea94a222af5ef2ee76df029c1d2
change-id: 20250923-uid_slot-e3559cf5ca30

Best regards,
-- 
Niklas Schnelle

[PATCH v7 1/2] docs: s390/pci: Improve and update PCI documentation

[Niklas Schnelle]

Update the s390 specific PCI documentation to better reflect current
behavior and terms such as the handling of Isolated VFs via commit
25f39d3dcb48 ("s390/pci: Ignore RID for isolated VFs").

Add a descriptions for /sys/firmware/clp/uid_is_unique which was added
in commit b043a81ce3ee ("s390/pci: Expose firmware provided UID Checking
state in sysfs") but missed documentation.

Similarly add documentation for the fidparm attribute added by commit
99ad39306a62 ("s390/pci: Expose FIDPARM attribute in sysfs") and
add a list of pft values and their names.

Finally improve formatting of the different attribute descriptions by
adding a separating colon.

Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
 Documentation/arch/s390/pci.rst | 144 +++++++++++++++++++++++++++-------------
 1 file changed, 97 insertions(+), 47 deletions(-)

diff --git a/Documentation/arch/s390/pci.rst b/Documentation/arch/s390/pci.rst
index d5755484d8e75c7bf67a350e61bbe04f0452a2fa..8cb0a1e784a7cfc5df1e04a4154ba02c9ecf46cc 100644
--- a/Documentation/arch/s390/pci.rst
+++ b/Documentation/arch/s390/pci.rst
@@ -6,6 +6,7 @@ S/390 PCI
 
 Authors:
         - Pierre Morel
+        - Niklas Schnelle
 
 Copyright, IBM Corp. 2020
 
@@ -27,14 +28,16 @@ Command line parameters
 debugfs entries
 ---------------
 
-The S/390 debug feature (s390dbf) generates views to hold various debug results in sysfs directories of the form:
+The S/390 debug feature (s390dbf) generates views to hold various debug results
+in sysfs directories of the form:
 
  * /sys/kernel/debug/s390dbf/pci_*/
 
 For example:
 
   - /sys/kernel/debug/s390dbf/pci_msg/sprintf
-    Holds messages from the processing of PCI events, like machine check handling
+
+    holds messages from the processing of PCI events, like machine check handling
     and setting of global functionality, like UID checking.
 
   Change the level of logging to be more or less verbose by piping
@@ -47,87 +50,134 @@ Sysfs entries
 
 Entries specific to zPCI functions and entries that hold zPCI information.
 
-* /sys/bus/pci/slots/XXXXXXXX
+* /sys/bus/pci/slots/XXXXXXXX:
 
-  The slot entries are set up using the function identifier (FID) of the
-  PCI function. The format depicted as XXXXXXXX above is 8 hexadecimal digits
-  with 0 padding and lower case hexadecimal digits.
+  The slot entries are set up using the function identifier (FID) of the PCI
+  function as slot name. The format depicted as XXXXXXXX above is 8 hexadecimal
+  digits with 0 padding and lower case hexadecimal digits.
 
   - /sys/bus/pci/slots/XXXXXXXX/power
 
   A physical function that currently supports a virtual function cannot be
   powered off until all virtual functions are removed with:
-  echo 0 > /sys/bus/pci/devices/XXXX:XX:XX.X/sriov_numvf
+  echo 0 > /sys/bus/pci/devices/DDDD:BB:dd.f/sriov_numvf
 
-* /sys/bus/pci/devices/XXXX:XX:XX.X/
+* /sys/bus/pci/devices/DDDD:BB:dd.f/:
 
-  - function_id
-    A zPCI function identifier that uniquely identifies the function in the Z server.
+  - function_id:
+    The zPCI function identifier (FID) is a 32-bit hexadecimal value that
+    uniquely identifies the PCI function. Unless the hypervisor provides
+    a virtual FID e.g. on KVM this identifier is unique across the machine even
+    between different partitions.
 
-  - function_handle
-    Low-level identifier used for a configured PCI function.
-    It might be useful for debugging.
+  - function_handle:
+    This 32-bit hexadecimal value is a low-level identifier used for a PCI
+    function. Note that the function handle may be changed and become invalid
+    on PCI events and when enabling/disabling the PCI function.
 
-  - pchid
-    Model-dependent location of the I/O adapter.
+  - pchid:
+    This 16-bit hexadecimal value encodes a model-dependent location for
+    the PCI function.
 
-  - pfgid
-    PCI function group ID, functions that share identical functionality
+  - pfgid:
+    PCI function group ID; functions that share identical functionality
     use a common identifier.
     A PCI group defines interrupts, IOMMU, IOTLB, and DMA specifics.
 
-  - vfn
+  - vfn:
     The virtual function number, from 1 to N for virtual functions,
     0 for physical functions.
 
-  - pft
-    The PCI function type
+  - pft:
+    The PCI function type is an s390-specific type attribute. It indicates
+    a more general, usage oriented, type than PCI Specification
+    class/vendor/device identifiers. That is PCI functions with the same pft
+    value may be backed by different hardware implementations. At the same time
+    apart from unclassified functions (pft is 0x00) the same pft value
+    generally implies a similar usage model. At the same time the same
+    PCI hardware device may appear with different pft values when in a
+    different usage model. For example NETD and NETH VFs may be implemented
+    by the same PCI hardware device but in NETD the parent Physical Function
+    is user managed while with NETH it is platform managed.
 
-  - port
-    The port corresponds to the physical port the function is attached to.
-    It also gives an indication of the physical function a virtual function
-    is attached to.
+    Currently the following PFT values are defined:
 
-  - uid
-    The user identifier (UID) may be defined as part of the machine
-    configuration or the z/VM or KVM guest configuration. If the accompanying
-    uid_is_unique attribute is 1 the platform guarantees that the UID is unique
-    within that instance and no devices with the same UID can be attached
-    during the lifetime of the system.
+    - 0x00 (UNC): Unclassified
+    - 0x02 (ROCE): RoCE Express
+    - 0x05 (ISM): Internal Shared Memory
+    - 0x0a (ROC2): RoCE Express 2
+    - 0x0b (NVMe): NVMe
+    - 0x0c (NETH): Network Express hybrid
+    - 0x0d (CNW): Cloud Network Adapter
+    - 0x0f (NETD): Network Express direct
 
-  - uid_is_unique
-    Indicates whether the user identifier (UID) is guaranteed to be and remain
-    unique within this Linux instance.
+  - port:
+    The port is a decimal value corresponding to the physical port the function
+    is attached to. Virtual Functions (VFs) share the port with their parent
+    Physical Function (PF). A value of 0 indicates that the port attribute is
+    not applicable for that PCI function type.
 
-  - pfip/segmentX
+  - uid:
+    The user-defined identifier (UID) for a PCI function is a 32-bit
+    hexadecimal value. It is defined on a per instance basis as part of the
+    partition, KVM guest, or z/VM guest configuration. If UID Checking is
+    enabled the platform ensures that the UID is unique within that instance
+    and no two PCI functions with the same UID will be visible to the instance.
+
+    Independent of this guarantee and unlike the function ID (FID) the UID may
+    be the same in different partitions within the same machine. This allows to
+    create PCI configurations in multiple partitions to be identical in the
+    UID-namespace.
+
+  - uid_is_unique:
+    A 0 or 1 flag indicating whether the user-defined identifier (UID) is
+    guaranteed to be and remain unique within this Linux instance. This
+    platform feature is called UID Checking.
+
+  - pfip/segmentX:
     The segments determine the isolation of a function.
     They correspond to the physical path to the function.
     The more the segments are different, the more the functions are isolated.
 
+  - fidparm:
+    Contains an 8-bit-per-PCI function parameter field in hexadecimal provided
+    by the platform. The meaning of this field is PCI function type specific.
+    For NETH VFs a value of 0x01 indicates that the function supports
+    promiscuous mode.
+
+* /sys/firmware/clp/uid_is_unique:
+
+  In addition to the per-device uid_is_unique attribute this presents a
+  global indication of whether UID Checking is enabled. This allows users
+  to check for UID Checking even when no PCI functions are configured.
+
 Enumeration and hotplug
 =======================
 
 The PCI address consists of four parts: domain, bus, device and function,
-and is of this form: DDDD:BB:dd.f
+and is of this form: DDDD:BB:dd.f.
 
-* When not using multi-functions (norid is set, or the firmware does not
-  support multi-functions):
+* For a PCI function for which the platform does not expose the RID, the
+  pci=norid kernel parameter is used, or a so-called isolated Virtual Function
+  which does have RID information but is used without its parent Physical
+  Function being part of the same PCI configuration:
 
   - There is only one function per domain.
 
-  - The domain is set from the zPCI function's UID as defined during the
-    LPAR creation.
+  - The domain is set from the zPCI function's UID if UID Checking is on;
+    otherwise the domain ID is generated dynamically and is not stable
+    across reboots or hot plug.
 
-* When using multi-functions (norid parameter is not set),
-  zPCI functions are addressed differently:
+* For a PCI function for which the platform exposes the RID and which
+  is not an Isolated Virtual Function:
 
   - There is still only one bus per domain.
 
-  - There can be up to 256 functions per bus.
+  - There can be up to 256 PCI functions per bus.
 
-  - The domain part of the address of all functions for
-    a multi-Function device is set from the zPCI function's UID as defined
-    in the LPAR creation for the function zero.
+  - The domain part of the address of all functions within the same topology is
+    that of the configured PCI function with the lowest devfn within that
+    topology.
 
-  - New functions will only be ready for use after the function zero
-    (the function with devfn 0) has been enumerated.
+  - Virtual Functions generated by an SR-IOV capable Physical Function only
+    become visible once SR-IOV is enabled.

-- 
2.51.0

[PATCH v7 2/2] PCI: s390: Expose the UID as an arch specific PCI slot attribute

[Niklas Schnelle]

On s390, an individual PCI function can generally be identified by two
identifiers, the FID and the UID. Which identifier is used depends on
the scope and the platform configuration.

The first identifier, the FID, is always available and identifies a PCI
device uniquely within a machine. The FID may be virtualized by
hypervisors, but on the LPAR level, the machine scope makes it
impossible to create the same configuration based on FIDs on two
different LPARs of the same machine, and difficult to reuse across
machines.

Such matching LPAR configurations are useful, though, allowing
standardized setups and booting a Linux installation on different LPARs.
To this end the UID, or user-defined identifier, was introduced. While
it is only guaranteed to be unique within an LPAR and only if indicated
by firmware, it allows users to replicate PCI device setups.

On s390, which uses a machine hypervisor, a per PCI function hotplug
model is used. The shortcoming with the UID then is, that it is not
visible to the user without first attaching the PCI function and
accessing the "uid" device attribute. The FID, on the other hand, is
used as the slot name and is thus known even with the PCI function in
standby.

Remedy this shortcoming by providing the UID as an attribute on the slot
allowing the user to identify a PCI function based on the UID without
having to first attach it. Do this via a macro mechanism analogous to
what was introduced by commit 265baca69a07 ("s390/pci: Stop usurping
pdev->dev.groups") for the PCI device attributes.

Reviewed-by: Gerd Bayer <gbayer@linux.ibm.com>
Reviewed-by: Julian Ruess <julianr@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
 Documentation/arch/s390/pci.rst |  7 +++++++
 arch/s390/include/asm/pci.h     |  4 ++++
 arch/s390/pci/pci_sysfs.c       | 20 ++++++++++++++++++++
 drivers/pci/slot.c              | 13 ++++++++++++-
 4 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/Documentation/arch/s390/pci.rst b/Documentation/arch/s390/pci.rst
index 8cb0a1e784a7cfc5df1e04a4154ba02c9ecf46cc..a620cf694c6f6c0bbd4f77ea4768cce7cc42c963 100644
--- a/Documentation/arch/s390/pci.rst
+++ b/Documentation/arch/s390/pci.rst
@@ -58,6 +58,13 @@ Entries specific to zPCI functions and entries that hold zPCI information.
 
   - /sys/bus/pci/slots/XXXXXXXX/power
 
+  In addition to using the FID as the name of the slot, the slot directory
+  also contains the following s390-specific slot attributes.
+
+  - uid:
+    The User-defined identifier (UID) of the function which may be configured
+    by this slot. See also the corresponding attribute of the device.
+
   A physical function that currently supports a virtual function cannot be
   powered off until all virtual functions are removed with:
   echo 0 > /sys/bus/pci/devices/DDDD:BB:dd.f/sriov_numvf
diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
index c0ff19dab5807c7e1aabb48a0e9436aac45ec97d..5dcf35f0f325f5f44b28109a1c8d9aef18401035 100644
--- a/arch/s390/include/asm/pci.h
+++ b/arch/s390/include/asm/pci.h
@@ -208,6 +208,10 @@ extern const struct attribute_group zpci_ident_attr_group;
 			    &pfip_attr_group,		 \
 			    &zpci_ident_attr_group,
 
+extern const struct attribute_group zpci_slot_attr_group;
+
+#define ARCH_PCI_SLOT_GROUPS (&zpci_slot_attr_group)
+
 extern unsigned int s390_pci_force_floating __initdata;
 extern unsigned int s390_pci_no_rid;
 
diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c
index c2444a23e26c4218832bb91930b5f0ffd498d28f..d98d97df792adb3c7e415a8d374cc2f3a65fbb52 100644
--- a/arch/s390/pci/pci_sysfs.c
+++ b/arch/s390/pci/pci_sysfs.c
@@ -187,6 +187,17 @@ static ssize_t index_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(index);
 
+static ssize_t zpci_uid_slot_show(struct pci_slot *slot, char *buf)
+{
+	struct zpci_dev *zdev = container_of(slot->hotplug, struct zpci_dev,
+					     hotplug_slot);
+
+	return sysfs_emit(buf, "0x%x\n", zdev->uid);
+}
+
+static struct pci_slot_attribute zpci_slot_attr_uid =
+	__ATTR(uid, 0444, zpci_uid_slot_show, NULL);
+
 static umode_t zpci_index_is_visible(struct kobject *kobj,
 				     struct attribute *attr, int n)
 {
@@ -243,6 +254,15 @@ const struct attribute_group pfip_attr_group = {
 	.attrs = pfip_attrs,
 };
 
+static struct attribute *zpci_slot_attrs[] = {
+	&zpci_slot_attr_uid.attr,
+	NULL,
+};
+
+const struct attribute_group zpci_slot_attr_group = {
+	.attrs = zpci_slot_attrs,
+};
+
 static struct attribute *clp_fw_attrs[] = {
 	&uid_checking_attr.attr,
 	NULL,
diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c
index 787311614e5b6ebb39e7284f9b9f205a0a684d6d..2f8fcfbbec24e73d0bb6e40fd04c05a94f518045 100644
--- a/drivers/pci/slot.c
+++ b/drivers/pci/slot.c
@@ -96,7 +96,18 @@ static struct attribute *pci_slot_default_attrs[] = {
 	&pci_slot_attr_cur_speed.attr,
 	NULL,
 };
-ATTRIBUTE_GROUPS(pci_slot_default);
+
+static const struct attribute_group pci_slot_default_group = {
+	.attrs = pci_slot_default_attrs,
+};
+
+static const struct attribute_group *pci_slot_default_groups[] = {
+	&pci_slot_default_group,
+#ifdef ARCH_PCI_SLOT_GROUPS
+	ARCH_PCI_SLOT_GROUPS,
+#endif
+	NULL,
+};
 
 static const struct kobj_type pci_slot_ktype = {
 	.sysfs_ops = &pci_slot_sysfs_ops,

-- 
2.51.0

Re: [PATCH v7 1/2] docs: s390/pci: Improve and update PCI documentation

[Gerd Bayer]

On Tue, 2026-04-07 at 12:12 +0200, Niklas Schnelle wrote:


[... snip ...]

> Similarly add documentation for the fidparm attribute added by commit
> 99ad39306a62 ("s390/pci: Expose FIDPARM attribute in sysfs") and
> add a list of pft values and their names.
> 

[... snip ...]

> ---
>  Documentation/arch/s390/pci.rst | 144 +++++++++++++++++++++++++++-------------
>  1 file changed, 97 insertions(+), 47 deletions(-)
> 
> diff --git a/Documentation/arch/s390/pci.rst b/Documentation/arch/s390/pci.rst
> index d5755484d8e75c7bf67a350e61bbe04f0452a2fa..8cb0a1e784a7cfc5df1e04a4154ba02c9ecf46cc 100644
> --- a/Documentation/arch/s390/pci.rst
> +++ b/Documentation/arch/s390/pci.rst
> @@ -6,6 +6,7 @@ S/390 PCI
>  
>  Authors:
>          - Pierre Morel
> +        - Niklas Schnelle
>  
>  Copyright, IBM Corp. 2020
>  
> @@ -27,14 +28,16 @@ Command line parameters
>  debugfs entries
>  ---------------
>  
> -The S/390 debug feature (s390dbf) generates views to hold various debug results in sysfs directories of the form:
> +The S/390 debug feature (s390dbf) generates views to hold various debug results
> +in sysfs directories of the form:
>  
>   * /sys/kernel/debug/s390dbf/pci_*/
>  
>  For example:
>  
>    - /sys/kernel/debug/s390dbf/pci_msg/sprintf
> -    Holds messages from the processing of PCI events, like machine check handling
> +
> +    holds messages from the processing of PCI events, like machine check handling
>      and setting of global functionality, like UID checking.
>  
>    Change the level of logging to be more or less verbose by piping
> @@ -47,87 +50,134 @@ Sysfs entries
>  

[... snip ...]

> +
> +* /sys/firmware/clp/uid_is_unique:

As much as I had loved the attribute to be named as such, or even
better /sys/firmware/clp/uids_are_unique, I find commit b043a81ce3ee
("s390/pci: Expose firmware provided UID Checking state in sysfs") has
introduced

/sys/firmware/clp/uid_checking.

Sorry, that this did slip me...

Gerd