powerpc/perf: Fix the check for SIAR value

[ Upstream commit 3c69a5f ]

Incase of random sampling, there can be scenarios where
Sample Instruction Address Register(SIAR) may not latch
to the sampled instruction and could result in
the value of 0. In these scenarios it is preferred to
return regs->nip. These corner cases are seen in the
previous generation (p9) also.

Patch adds the check for SIAR value along with regs_use_siar
and siar_valid checks so that the function will return
regs->nip incase SIAR is zero.

Patch drops the code under PPMU_P10_DD1 flag check
which handles SIAR 0 case only for Power10 DD1.

Fixes: 2ca13a4 ("powerpc/perf: Use regs->nip when SIAR is zero")
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210818171556.36912-3-kjain@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/powerpc/perf/core-book3s.c

@@ -2251,18 +2251,10 @@ 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 (ppmu && (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
+	if (regs_use_siar(regs) && siar_valid(regs) && siar)
+		return siar + perf_ip_adjust(regs);
 	else
 		return regs->nip;
 }