powerpc/rtas: add tracepoints around RTAS entry

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 <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-11-26929c8cce78@linux.ibm.com

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index d2622b997b68f9a2d788b0e8438a1c9ff54242a3..a6d0c46b45127b4a0b4c95926cf89dea6a56ccf3 100644 (file)
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -38,6 +38,7 @@
 #include <asm/page.h>
 #include <asm/rtas.h>
 #include <asm/time.h>
+#include <asm/trace.h>
 #include <asm/udbg.h>
 
 struct rtas_filter {
@@ -523,24 +524,70 @@ static const struct rtas_function *rtas_token_to_function(s32 token)
 /* This is here deliberately so it's only used in this file */
 void enter_rtas(unsigned long);
 
-static void do_enter_rtas(struct rtas_args *args)
+static void __do_enter_rtas(struct rtas_args *args)
+{
+       enter_rtas(__pa(args));
+       srr_regs_clobbered(); /* rtas uses SRRs, invalidate */
+}
+
+static void __do_enter_rtas_trace(struct rtas_args *args)
 {
-       unsigned long msr;
+       const char *name = NULL;
+       /*
+        * If the tracepoints that consume the function name aren't
+        * active, avoid the lookup.
+        */
+       if ((trace_rtas_input_enabled() || trace_rtas_output_enabled())) {
+               const s32 token = be32_to_cpu(args->token);
+               const struct rtas_function *func = rtas_token_to_function(token);
+
+               name = func->name;
+       }
+
+       trace_rtas_input(args, name);
+       trace_rtas_ll_entry(args);
+
+       __do_enter_rtas(args);
 
+       trace_rtas_ll_exit(args);
+       trace_rtas_output(args, name);
+}
+
+static void do_enter_rtas(struct rtas_args *args)
+{
+       const unsigned long msr = mfmsr();
+       /*
+        * Situations where we want to skip any active tracepoints for
+        * safety reasons:
+        *
+        * 1. The last code executed on an offline CPU as it stops,
+        *    i.e. we're about to call stop-self. The tracepoints'
+        *    function name lookup uses xarray, which uses RCU, which
+        *    isn't valid to call on an offline CPU.  Any events
+        *    emitted on an offline CPU will be discarded anyway.
+        *
+        * 2. In real mode, as when invoking ibm,nmi-interlock from
+        *    the pseries MCE handler. We cannot count on trace
+        *    buffers or the entries in rtas_token_to_function_xarray
+        *    to be contained in the RMO.
+        */
+       const unsigned long mask = MSR_IR | MSR_DR;
+       const bool can_trace = likely(cpu_online(raw_smp_processor_id()) &&
+                                     (msr & mask) == mask);
        /*
         * Make sure MSR[RI] is currently enabled as it will be forced later
         * in enter_rtas.
         */
-       msr = mfmsr();
        BUG_ON(!(msr & MSR_RI));
 
        BUG_ON(!irqs_disabled());
 
        hard_irq_disable(); /* Ensure MSR[EE] is disabled on PPC64 */
 
-       enter_rtas(__pa(args));
-
-       srr_regs_clobbered(); /* rtas uses SRRs, invalidate */
+       if (can_trace)
+               __do_enter_rtas_trace(args);
+       else
+               __do_enter_rtas(args);
 }
 
 struct rtas_t rtas;