From 8cfaf106918a8c13abb24c641556172afbb9545c Mon Sep 17 00:00:00 2001
From: Michael Ellerman <mpe@ellerman.id.au>
Date: Mon, 11 Feb 2019 11:20:01 +1100
Subject: [PATCH] powerpc/64s: Fix logic when handling unknown CPU features
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References: bsc#1055117
Patch-mainline: v5.1-rc1
Git-commit: 8cfaf106918a8c13abb24c641556172afbb9545c

In cpufeatures_process_feature(), if a provided CPU feature is unknown and
enable_unknown is false, we erroneously print that the feature is being
enabled and return true, even though no feature has been enabled, and
may also set feature bits based on the last entry in the match table.

Fix this so that we only set feature bits from the match table if we have
actually enabled a feature from that table, and when failing to enable an
unknown feature, always print the "not enabling" message and return false.

Coincidentally, some older gccs (<GCC 7), when invoked with
-fsanitize-coverage=trace-pc, cause a spurious uninitialised variable
warning in this function:

  arch/powerpc/kernel/dt_cpu_ftrs.c: In function ‘cpufeatures_process_feature’:
  arch/powerpc/kernel/dt_cpu_ftrs.c:686:7: warning: ‘m’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    if (m->cpu_ftr_bit_mask)

An upcoming patch will enable support for kcov, which requires this option.
This patch avoids the warning.

Fixes: 5a61ef74f269 ("powerpc/64s: Support new device tree binding for discovering CPU features")
Reported-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[ajd: add commit message]
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/kernel/dt_cpu_ftrs.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
index 8be3721d9302..e49bd5efcfe6 100644
--- a/arch/powerpc/kernel/dt_cpu_ftrs.c
+++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
@@ -666,8 +666,10 @@ static bool __init cpufeatures_process_feature(struct dt_cpu_feature *f)
 		m = &dt_cpu_feature_match_table[i];
 		if (!strcmp(f->name, m->name)) {
 			known = true;
-			if (m->enable(f))
+			if (m->enable(f)) {
+				cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
 				break;
+			}
 
 			pr_info("not enabling: %s (disabled or unsupported by kernel)\n",
 				f->name);
@@ -675,17 +677,12 @@ static bool __init cpufeatures_process_feature(struct dt_cpu_feature *f)
 		}
 	}
 
-	if (!known && enable_unknown) {
-		if (!feat_try_enable_unknown(f)) {
-			pr_info("not enabling: %s (unknown and unsupported by kernel)\n",
-				f->name);
-			return false;
-		}
+	if (!known && (!enable_unknown || !feat_try_enable_unknown(f))) {
+		pr_info("not enabling: %s (unknown and unsupported by kernel)\n",
+			f->name);
+		return false;
 	}
 
-	if (m->cpu_ftr_bit_mask)
-		cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
-
 	if (known)
 		pr_debug("enabling: %s\n", f->name);
 	else
-- 
2.20.1