powerpc/rtas: arch-wide function token lookup conversions

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 <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-20-26929c8cce78@linux.ibm.com

arch/powerpc/xmon/xmon.c

@@ -76,9 +76,6 @@ static cpumask_t xmon_batch_cpus = CPU_MASK_NONE;
 #define xmon_owner 0
 #endif /* CONFIG_SMP */
 
-#ifdef CONFIG_PPC_PSERIES
-static int set_indicator_token = RTAS_UNKNOWN_SERVICE;
-#endif
 static unsigned long in_xmon __read_mostly = 0;
 static int xmon_on = IS_ENABLED(CONFIG_XMON_DEFAULT);
 static bool xmon_is_ro = IS_ENABLED(CONFIG_XMON_DEFAULT_RO_MODE);
@@ -398,6 +395,7 @@ static inline void disable_surveillance(void)
 #ifdef CONFIG_PPC_PSERIES
 	/* Since this can't be a module, args should end up below 4GB. */
 	static struct rtas_args args;
+	const s32 token = rtas_function_token(RTAS_FN_SET_INDICATOR);
 
 	/*
 	 * At this point we have got all the cpus we can into
@@ -406,10 +404,10 @@ static inline void disable_surveillance(void)
 	 * If we did try to take rtas.lock there would be a
 	 * real possibility of deadlock.
 	 */
-	if (set_indicator_token == RTAS_UNKNOWN_SERVICE)
+	if (token == RTAS_UNKNOWN_SERVICE)
 		return;
 
-	rtas_call_unlocked(&args, set_indicator_token, 3, 1, NULL,
+	rtas_call_unlocked(&args, token, 3, 1, NULL,
 			   SURVEILLANCE_TOKEN, 0, 0);
 
 #endif /* CONFIG_PPC_PSERIES */
@@ -3976,14 +3974,6 @@ static void xmon_init(int enable)
 		__debugger_iabr_match = xmon_iabr_match;
 		__debugger_break_match = xmon_break_match;
 		__debugger_fault_handler = xmon_fault_handler;
-
-#ifdef CONFIG_PPC_PSERIES
-		/*
-		 * Get the token here to avoid trying to get a lock
-		 * during the crash, causing a deadlock.
-		 */
-		set_indicator_token = rtas_token("set-indicator");
-#endif
 	} else {
 		__debugger = NULL;
 		__debugger_ipi = NULL;