powerpc/pseries/ras: Avoid calling rtas_token() in NMI paths

In the interest of reducing code and possible failures in the
machine check and system reset paths, grab the "ibm,nmi-interlock"
token at init time.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Link: https://lore.kernel.org/r/20200508043408.886394-6-npiggin@gmail.com

arch/powerpc/include/asm/firmware.h

@@ -128,6 +128,7 @@ extern void machine_check_fwnmi(void);
 
 /* This is true if we are using the firmware NMI handler (typically LPAR) */
 extern int fwnmi_active;
+extern int ibm_nmi_interlock_token;
 
 extern unsigned int __start___fw_ftr_fixup, __stop___fw_ftr_fixup;
 

arch/powerpc/platforms/pseries/ras.c

@@ -458,7 +458,7 @@ static struct rtas_error_log *fwnmi_get_errinfo(struct pt_regs *regs)
  */
 static void fwnmi_release_errinfo(void)
 {
-	int ret = rtas_call(rtas_token("ibm,nmi-interlock"), 0, 1, NULL);
+	int ret = rtas_call(ibm_nmi_interlock_token, 0, 1, NULL);
 	if (ret != 0)
 		printk(KERN_ERR "FWNMI: nmi-interlock failed: %d\n", ret);
 }

arch/powerpc/platforms/pseries/setup.c

@@ -84,6 +84,7 @@ unsigned long CMO_PageSize = (ASM_CONST(1) << IOMMU_PAGE_SHIFT_4K);
 EXPORT_SYMBOL(CMO_PageSize);
 
 int fwnmi_active;  /* TRUE if an FWNMI handler is present */
+int ibm_nmi_interlock_token;
 
 static void pSeries_show_cpuinfo(struct seq_file *m)
 {
@@ -114,9 +115,14 @@ static void __init fwnmi_init(void)
 	struct slb_entry *slb_ptr;
 	size_t size;
 #endif
+	int ibm_nmi_register_token;
 
-	int ibm_nmi_register = rtas_token("ibm,nmi-register");
-	if (ibm_nmi_register == RTAS_UNKNOWN_SERVICE)
+	ibm_nmi_register_token = rtas_token("ibm,nmi-register");
+	if (ibm_nmi_register_token == RTAS_UNKNOWN_SERVICE)
+		return;
+
+	ibm_nmi_interlock_token = rtas_token("ibm,nmi-interlock");
+	if (WARN_ON(ibm_nmi_interlock_token == RTAS_UNKNOWN_SERVICE))
 		return;
 
 	/* If the kernel's not linked at zero we point the firmware at low
@@ -124,8 +130,8 @@ static void __init fwnmi_init(void)
 	system_reset_addr  = __pa(system_reset_fwnmi) - PHYSICAL_START;
 	machine_check_addr = __pa(machine_check_fwnmi) - PHYSICAL_START;
 
-	if (0 == rtas_call(ibm_nmi_register, 2, 1, NULL, system_reset_addr,
-				machine_check_addr))
+	if (0 == rtas_call(ibm_nmi_register_token, 2, 1, NULL,
+			   system_reset_addr, machine_check_addr))
 		fwnmi_active = 1;
 
 	/*