powerpc/pseries: Add papr-indices char driver for ibm,get-indices

The RTAS call ibm,get-indices is used to obtain indices and
location codes for a specified indicator or sensor token. The
current implementation uses rtas_get_indices() API provided by
librtas library which allocates RMO buffer and issue this RTAS
call in the user space. But writable mapping /dev/mem access by
the user space is prohibited under system lockdown.

To overcome the restricted access in the user space, the kernel
provide interfaces to collect indices data from the hypervisor.
This patch adds papr-indices character driver and expose standard
interfaces such as open / ioctl/ read to user space in ways that
are compatible with lockdown.

PAPR (2.13 7.3.17 ibm,get-indices RTAS Call) describes the
following steps to retrieve all indices data:
- User input parameters to the RTAS call: sensor or indicator,
  and indice type
- ibm,get-indices is sequence RTAS call which means has to issue
  multiple times to get the entire list of indicators or sensors
  of a particular type. The hypervisor expects the first RTAS call
  with the sequence 1 and the subsequent calls with the sequence
  number returned from the previous calls.
- The OS may not interleave calls to ibm,get-indices for different
  indicator or sensor types. Means other RTAS calls with different
  type should not be issued while the previous type sequence is in
  progress. So collect the entire list of indices and copied to
  buffer BLOB during ioctl() and expose this buffer to the user
  space with the file descriptor.
- The hypervisor fills the work area with a specific format but
  does not return the number of bytes written to the buffer.
  Instead of parsing the data for each call to determine the data
  length, copy the work area size (RTAS_GET_INDICES_BUF_SIZE) to
  the buffer. Return work-area size of data to the user space for
  each read() call.

Expose these interfaces to user space with a /dev/papr-indices
character device using the following programming model:

 int devfd = open("/dev/papr-indices", O_RDONLY);
 int fd = ioctl(devfd, PAPR_INDICES_IOC_GET,
		struct papr_indices_io_block)
  - Collect all indices data for the specified token to the buffer
 char *buf = malloc(RTAS_GET_INDICES_BUF_SIZE);
 length = read(fd, buf,  RTAS_GET_INDICES_BUF_SIZE)
  - RTAS_GET_INDICES_BUF_SIZE of data is returned to the user
    space.
  - The user space retrieves the indices and their location codes
    from the buffer
  - Should issue multiple read() calls until reaches the end of
    BLOB buffer.

The read() should use the file descriptor obtained from ioctl to
get the data that is exposed to file descriptor. Implemented
support in librtas (rtas_get_indices()) for this new ABI for
system lockdown.

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Tested-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250416225743.596462-4-haren@linux.ibm.com

0 files changed, 0 insertions, 0 deletions