[PATCH 0/3] s390/cio: Harden pmcw/schib handling for dnv=0

[Vineeth Vijayan <vneethv@linux.ibm.com>]

For I/O subchannels, pmcw.dnv must be validated before relying on any
other PMCW or SCHIB fields.
Two issues exist today:
 - Some I/O entry points check pmcw.ena without first verifying that
   pmcw.dnv is set.
 - cio_update_schib() updates the cached SCHIB before validating
   pmcw.dnv, allowing an stsch result with dnv=0 to leave stale or
   undefined data in sch->schib.
 
This can trigger spurious, non-fatal error messages in the guest kernel
log when a virtio device is being detached.
 
Fix this by validating pmcw.dnv before updating the cached SCHIB. Also
clear the cached SCHIB when stsch succeeds but returns dnv=0, ensuring
that stale state is not retained.
 
Additionally, add pmcw.dnv checks before pmcw.ena checks in I/O entry
points and return -ENODEV when no device is present. Guard remaining
direct accesses to cached PMCW fields, such as chpid[] and pam, to
ensure they are only evaluated when the SCHIB contents are valid.
 
This was reported and discussed at:
 
Link: https://lore.kernel.org/linux-s390/20260612155407.199218-1-wbezenah@linux.ibm.com/ 

Vineeth Vijayan (3):
  s390/cio: Fix cio_update_schib() to not cache invalid schib
  s390/cio: Check pmcw.dnv before pmcw.ena in I/O entry points
  s390/cio: Guard PMCW field accesses with dnv check

 drivers/s390/cio/chp.c          |  3 +++
 drivers/s390/cio/cio.c          | 11 +++++++----
 drivers/s390/cio/device.c       |  9 +++++----
 drivers/s390/cio/device_fsm.c   |  3 +++
 drivers/s390/cio/device_ops.c   | 21 +++++++++++++++++++++
 drivers/s390/cio/vfio_ccw_fsm.c |  2 +-
 6 files changed, 40 insertions(+), 9 deletions(-)

-- 
2.53.0