linux-toradex.git/arch/powerpc/kernel/rtas.c, branch v6.7

powerpc/rtas: export rtas_error_rc() for reuse.

2023-08-18T13:28:57+00:00

Also, #define descriptive names for common rtas return codes and use it
instead of numeric values.

Signed-off-by: Mahesh Salgaonkar 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/169235811556.193557.1023625262204809514.stgit@jupiter

powerpc/fadump: invoke ibm,os-term with rtas_call_unlocked()

2023-08-18T10:25:52+00:00

Invoke ibm,os-term call with rtas_call_unlocked(), without using the
RTAS spinlock, to avoid deadlock in the unlikely event of a machine
crash while making an RTAS call.

Signed-off-by: Hari Bathini 
Reviewed-by: Mahesh Salgaonkar 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230609071404.425529-1-hbathini@linux.ibm.com

powerpc/rtas: lockdep annotations

2023-03-30T12:36:35+00:00

Add lockdep annotations for the following properties that must hold:

* Any error log retrieval must be atomically coupled with the prior
  RTAS call, without a window for another RTAS call to occur before the
  error log can be retrieved.

* All users of the core rtas_args parameter block must hold rtas_lock.

Move the definitions of rtas_lock and rtas_args up in the file so that
__do_enter_rtas_trace() can refer to them.

Signed-off-by: Nathan Lynch 
Reviewed-by: Andrew Donnellan 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230220-rtas-queue-for-6-4-v1-6-010e4416f13f@linux.ibm.com

powerpc/rtas: fix miswording in rtas_function kerneldoc

2023-03-30T12:36:35+00:00

The 'filter' member is a pointer, not a bool; fix the wording
accordingly.

Signed-off-by: Nathan Lynch 
Reviewed-by: Andrew Donnellan 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230220-rtas-queue-for-6-4-v1-4-010e4416f13f@linux.ibm.com

powerpc/rtas: rtas_call_unlocked() kerneldoc

2023-03-30T12:36:34+00:00

Add documentation for rtas_call_unlocked(), including details on how
it differs from rtas_call().

Signed-off-by: Nathan Lynch 
Reviewed-by: Andrew Donnellan 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230220-rtas-queue-for-6-4-v1-3-010e4416f13f@linux.ibm.com

powerpc/rtas: use memmove for potentially overlapping buffer copy

2023-03-30T12:36:34+00:00

Using memcpy() isn't safe when buf is identical to rtas_err_buf, which
can happen during boot before slab is up. Full context which may not
be obvious from the diff:

	if (altbuf) {
		buf = altbuf;
	} else {
		buf = rtas_err_buf;
		if (slab_is_available())
			buf = kmalloc(RTAS_ERROR_LOG_MAX, GFP_ATOMIC);
	}
	if (buf)
		memcpy(buf, rtas_err_buf, RTAS_ERROR_LOG_MAX);

This was found by inspection and I'm not aware of it causing problems
in practice. It appears to have been introduced by commit
033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel"); the
old ppc64 version of this code did not have this problem.

Use memmove() instead.

Fixes: 033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel")
Signed-off-by: Nathan Lynch 
Reviewed-by: Andrew Donnellan 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230220-rtas-queue-for-6-4-v1-2-010e4416f13f@linux.ibm.com

powerpc/rtas: arch-wide function token lookup conversions

2023-02-13T11:35:03+00:00

With the tokens for all implemented RTAS functions now available via
rtas_function_token(), which is optimal and safe for arbitrary
contexts, there is no need to use rtas_token() or cache its result.

Most conversions are trivial, but a few are worth describing in more
detail:

* Error injection token comparisons for lockdown purposes are
  consolidated into a simple predicate: token_is_restricted_errinjct().

* A couple of special cases in block_rtas_call() do not use
  rtas_token() but perform string comparisons against names in the
  function table. These are converted to compare against token values
  instead, which is logically equivalent but less expensive.

* The lookup for the ibm,os-term token can be deferred until needed,
  instead of caching it at boot to avoid device tree traversal during
  panic.

* Since rtas_function_token() accesses a read-only data structure
  without taking any locks, xmon's lookup of set-indicator can be
  performed as needed instead of cached at startup.

Signed-off-by: Nathan Lynch 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-20-26929c8cce78@linux.ibm.com

powerpc/rtas: introduce rtas_function_token() API

2023-02-13T11:35:03+00:00

Users of rtas_token() supply a string argument that can't be validated
at build time. A typo or misspelling has to be caught by inspection or
by observing wrong behavior at runtime.

Since the core RTAS code now has consolidated the names of all
possible RTAS functions and mapped them to their tokens, token lookup
can be implemented using symbolic constants to index a static array.

So introduce rtas_function_token(), a replacement API which does that,
along with a rtas_service_present()-equivalent helper,
rtas_function_implemented(). Callers supply an opaque predefined
function handle which is used internally to index the function
table. Typos or other inappropriate arguments yield build errors, and
the function handle is a type that can't be easily confused with RTAS
tokens or other integer types.

Signed-off-by: Nathan Lynch 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-19-26929c8cce78@linux.ibm.com

powerpc/pseries: add RTAS work area allocator

2023-02-13T11:35:02+00:00

Various pseries-specific RTAS functions take a temporary "work area"
parameter - a buffer in memory accessible to RTAS. Typically such
functions are passed the statically allocated rtas_data_buf buffer as
the argument. This buffer is protected by a global spinlock. So users
of rtas_data_buf cannot perform sleeping operations while accessing
the buffer.

Most RTAS functions that have a work area parameter can return a
status (-2/990x) that indicates that the caller should retry. Before
retrying, the caller may need to reschedule or sleep (see
rtas_busy_delay() for details). This combination of factors
leads to uncomfortable constructions like this:

	do {
		spin_lock(&rtas_data_buf_lock);
		rc = rtas_call(token, __pa(rtas_data_buf, ...);
		if (rc == 0) {
			/* parse or copy out rtas_data_buf contents */
		}
		spin_unlock(&rtas_data_buf_lock);
	} while (rtas_busy_delay(rc));

Another unfortunately common way of handling this is for callers to
blithely ignore the possibility of a -2/990x status and hope for the
best.

If users were allowed to perform blocking operations while owning a
work area, the programming model would become less tedious and
error-prone. Users could schedule away, sleep, or perform other
blocking operations without having to release and re-acquire
resources.

We could continue to use a single work area buffer, and convert
rtas_data_buf_lock to a mutex. But that would impose an unnecessarily
coarse serialization on all users. As awkward as the current design
is, it prevents longer running operations that need to repeatedly use
rtas_data_buf from blocking the progress of others.

There are more considerations. One is that while 4KB is fine for all
current in-kernel uses, some RTAS calls can take much smaller buffers,
and some (VPD, platform dumps) would likely benefit from larger
ones. Another is that at least one RTAS function (ibm,get-vpd)
has *two* work area parameters. And finally, we should expect the
number of work area users in the kernel to increase over time as we
introduce lockdown-compatible ABIs to replace less safe use cases
based on sys_rtas/librtas.

So a special-purpose allocator for RTAS work area buffers seems worth
trying.

Properties:

* The backing memory for the allocator is reserved early in boot in
  order to satisfy RTAS addressing requirements, and then managed with
  genalloc.
* Allocations can block, but they never fail (mempool-like).
* Prioritizes first-come, first-serve fairness over throughput.
* Early boot allocations before the allocator has been initialized are
  served via an internal static buffer.

Intended to replace rtas_data_buf. New code that needs RTAS work area
buffers should prefer this API.

Signed-off-by: Nathan Lynch 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-12-26929c8cce78@linux.ibm.com

powerpc/rtas: add tracepoints around RTAS entry

2023-02-13T11:35:02+00:00

Decompose the RTAS entry C code into tracing and non-tracing variants,
calling the just-added tracepoints in the tracing-enabled path. Skip
tracing in contexts known to be unsafe (real mode, CPU offline).

Signed-off-by: Nathan Lynch 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-11-26929c8cce78@linux.ibm.com