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

[Ilpo Järvinen]

On Wed, 8 Jul 2026, Muralidhara M K wrote:

> 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.

Hi,

Could we have xx_locked() variant function for hsmp_test() to use so the 
recursive locking problem is avoided?

>  - 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
> 

-- 
 i.