powerpc/perf: Use regs->nip when SIAR is zero

In power10 DD1, there is an issue where the SIAR (Sampled Instruction
Address Register) is not latching to the sampled address during random
sampling. This results in value of 0s in the SIAR. Add a check to use
regs->nip when SIAR is zero.
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201021085329.384535-5-maddy@linux.ibm.com

arch/powerpc/perf/core-book3s.c

@@ -263,9 +263,16 @@ static inline u32 perf_get_misc_flags(struct pt_regs *regs)
 	 * DD1.
 	 */
 	if (marked && (ppmu->flags & PPMU_P10_DD1)) {
-		if (is_kernel_addr(mfspr(SPRN_SIAR)))
-			return PERF_RECORD_MISC_KERNEL;
-		return PERF_RECORD_MISC_USER;
+		unsigned long siar = mfspr(SPRN_SIAR);
+		if (siar) {
+			if (is_kernel_addr(siar))
+				return PERF_RECORD_MISC_KERNEL;
+			return PERF_RECORD_MISC_USER;
+		} else {
+			if (is_kernel_addr(regs->nip))
+				return PERF_RECORD_MISC_KERNEL;
+			return PERF_RECORD_MISC_USER;
+		}
 	}
 
 	/*
@@ -2199,8 +2206,14 @@ unsigned long perf_misc_flags(struct pt_regs *regs)
 unsigned long perf_instruction_pointer(struct pt_regs *regs)
 {
 	bool use_siar = regs_use_siar(regs);
+	unsigned long siar = mfspr(SPRN_SIAR);
 
-	if (use_siar && siar_valid(regs))
+	if (ppmu->flags & PPMU_P10_DD1) {
+		if (siar)
+			return siar;
+		else
+			return regs->nip;
+	} else if (use_siar && siar_valid(regs))
 		return mfspr(SPRN_SIAR) + perf_ip_adjust(regs);
 	else if (use_siar)
 		return 0;		// no valid instruction pointer