[PATCH v4 0/6] platform/x86/amd/hsmp: Serialize the data plane against socket teardown

[Muralidhara M K]

This series makes the AMD HSMP driver safe against concurrent probe/remove
of its per-socket devices and against the lock-free data plane (open
/dev/hsmp fds and hwmon/sysfs reads) racing socket teardown.

The ACPI front-end binds one platform device per socket but shares a single
socket array and a single /dev/hsmp misc device across them, while the data
plane issues mailbox messages with no coordination with driver teardown.
misc_deregister() does not drain already-open fds, so an in-flight message
can touch a freed socket array or an unmapped mailbox on unbind.

The fix is built up in small, bisectable steps:

 1. Serialize the ACPI probe/remove handshake with a dedicated mutex.
 2. Map the metric table with ioremap() and release it via a devres action,
    so its lifetime is no longer pinned to a single per-socket devres scope.
 3. Serialize the per-socket metric-table fill-and-copy with a mutex.
 4. Clear mdev.this_device on deregister (independent hygiene fix that the
    next patch relies on to track /dev/hsmp registration).
 5. Track shared socket ownership with a refcount and a single coordinated
    release helper, drop the is_probed flag and unparent /dev/hsmp.
 6. Add hsmp_sock_rwsem: the data plane holds it for read, a teardown path
    holds it for write to drain in-flight messages before freeing the socket
    array or unmapping the mailbox.

Each patch builds on its own and the series is checkpatch --strict clean.

Changes since v3:
 - Use guard()/scoped locking consistently for both the probe mutex and the
   data-plane rwsem, from the first patch that introduces each lock.
 - Platform teardown now uses devm_add_action_or_reset(): the metric-table
   unmap and the per-socket mutex destroy run from a single devres action
   instead of explicit remove()/probe-failure code. The ACPI array is shared
   across per-socket devices and must outlive an individual unbind, so it
   stays on explicit teardown.
 - Split the mdev.this_device clear into its own patch (new patch 4).
 - Drop dead defensive checks: the !sock guard in hsmp_unmap_metric_tbls()
   and the if (sock) in hsmp_acpi_remove(). Keep and document the one in the
   probe-failure path, where sock can legitimately be NULL.
 - Replace the !--refs construct with a plain decrement-then-test.
 - Explain why the probe path uses a separate mutex rather than the rwsem
   write side: the probe path itself drives the data plane via hsmp_test(),
   which takes the rwsem for read, so holding it for write across probe
   would deadlock.
 - Comment cleanups: drop history and "patch N" references, drop
   parenthetical function asides, single space after periods.

Muralidhara M K (6):
  platform/x86/amd/hsmp: Serialize ACPI HSMP is_probed with a probe
    mutex
  platform/x86/amd/hsmp: Map the metric table with ioremap() and unmap
    it explicitly
  platform/x86/amd/hsmp: Serialize per-socket metric table reads with a
    mutex
  platform/x86/amd/hsmp: Clear mdev.this_device on deregister
  platform/x86/amd/hsmp: ACPI HSMP refcounted sockets and coordinated
    release
  platform/x86/amd/hsmp: Serialize the data plane against socket
    teardown

 drivers/platform/x86/amd/hsmp/acpi.c | 135 ++++++++++++++++++++++++---
 drivers/platform/x86/amd/hsmp/hsmp.c | 107 ++++++++++++++++++++-
 drivers/platform/x86/amd/hsmp/hsmp.h |  15 ++-
 drivers/platform/x86/amd/hsmp/plat.c |  26 ++++++
 4 files changed, 265 insertions(+), 18 deletions(-)


base-commit: ff7836fa850c2f815bc219f1e48f6ec8699f4ae7
-- 
2.34.1