platform/x86/amd/hsmp: Add IOCTL_GET_TELEMETRY_DATA for metric table reads

The metric table needs to be delivered to userspace as a single
atomic snapshot, but the current sysfs metrics_bin path is a file
read: userspace can read it in chunks and observe a torn snapshot
if an SMU refresh happens between read() calls. The same path is
also bounded by PAGE_SIZE, so the ~13 KB table used by HSMP protocol
version 7 on Family 1Ah Model 50h-5Fh cannot be returned at all,
regardless of how userspace reads it. Rather than extend sysfs to
lift both restrictions, expose the metric table through the
existing HSMP character device using a new ioctl that always copies
the table in one shot.

Add struct hsmp_telemetry_data and HSMP_IOCTL_GET_TELEMETRY_DATA
to the UAPI header. Under the surrounding #pragma pack(4), placing
the __u64 user pointer first gives a tight 16-byte layout that is
identical for 32- and 64-bit callers, and the trailing __u16
reserved field is rejected with -EINVAL if non-zero so future
kernels can repurpose it without breaking already-deployed
userspace. The command is encoded with _IOW because the kernel only
reads the request struct; the snapshot travels through the user
pointer it carries.

The requested size may be anything from one byte up to the size
firmware reported for that socket's table. A short request returns
the leading bytes of the snapshot, so userspace built against an
older table layout keeps working on firmware that grew the table,
mirroring the relaxed response_sz rule applied to HSMP messages
earlier in this series. A request larger than the firmware table is
rejected with -EINVAL rather than short-written, so a caller can
never mistake a partial copy for a full one.

Dispatch hsmp_ioctl() on the ioctl command: the existing message
handler is factored out as hsmp_ioctl_msg() for HSMP_IOCTL_CMD, and
HSMP_IOCTL_GET_TELEMETRY_DATA goes to a new
hsmp_ioctl_get_telemetry() helper.

/dev/hsmp is a singleton character device that outlives an
individual socket unbind, so an ioctl issued on an already-open fd
can run concurrently with socket teardown. hsmp_sock_rwsem is the
driver's contract for that: the data plane takes it for read, and
probe and remove take it for write to drain the data plane before
freeing the socket array, unmapping the metric tables and
destroying the per-socket mutexes. hsmp_ioctl_get_telemetry() takes
it for read across the socket lookup, the checks on that socket's
metric-table state and the table read itself, so none of that state
can be torn down underneath it. Without this the handler would
sleep in its kvmalloc() holding no lock at all, and could resume
with a freed socket, locking a destroyed mutex and reading from an
unmapped iomem region.

The lock is dropped before the copy_to_user(), because faulting in
the destination can block indefinitely on a userfaultfd-backed
buffer and would otherwise leave a socket unbind waiting for the
write lock.

Since hsmp_metric_tbl_read() reached the mailbox through
hsmp_send_message(), which takes hsmp_sock_rwsem itself, calling it
with the lock already held would recursively take the read side and
can deadlock against a queued writer. Split out
hsmp_metric_tbl_read_locked(), which asserts the lock and uses
hsmp_send_message_locked(), and leave hsmp_metric_tbl_read() as a
wrapper that takes the read lock for the sysfs callers. This also
brings the whole fill-and-copy under the rwsem for those callers,
where the memcpy_fromio() previously ran outside it, and makes the
lock order uniformly hsmp_sock_rwsem -> metric_read_lock ->
hsmp_sem.

The user-controlled socket index in HSMP_IOCTL_GET_TELEMETRY_DATA is
clamped with array_index_nospec() before indexing hsmp_pdev.sock[],
mitigating Spectre v1 (CVE-2017-5753). Include linux/nospec.h, which
the file relied on getting transitively.

Co-developed-by: Muthusamy Ramalingam <muthusamy.ramalingam@amd.com>
Signed-off-by: Muthusamy Ramalingam <muthusamy.ramalingam@amd.com>
Signed-off-by: Muralidhara M K <muralidhara.mk@amd.com>
Link: https://patch.msgid.link/20260727141542.3370108-5-muralidhara.mk@amd.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

0 files changed, 0 insertions, 0 deletions