arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs

Instead of applying a CPU-specific workaround to all CPUs in the system,
allow it to only affect a subset of them (typical big-little case).

This is done by turning the erratum pointer into a per-CPU variable.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 30 insertions, 12 deletions

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index a0c9ee80147e..4551587bcb44 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -235,7 +235,8 @@ static u64 notrace hisi_161010101_read_cntvct_el0(void)
 #endif
 
 #ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND
-const struct arch_timer_erratum_workaround *timer_unstable_counter_workaround = NULL;
+DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *,
+               timer_unstable_counter_workaround);
 EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);
 
 DEFINE_STATIC_KEY_FALSE(arch_timer_read_ool_enabled);
@@ -338,9 +339,18 @@ arch_timer_iterate_errata(enum arch_timer_erratum_match_type type,
 }
 
 static
-void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa)
+void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa,
+                                  bool local)
 {
-        timer_unstable_counter_workaround = wa;
+        int i;
+
+        if (local) {
+                __this_cpu_write(timer_unstable_counter_workaround, wa);
+        } else {
+                for_each_possible_cpu(i)
+                        per_cpu(timer_unstable_counter_workaround, i) = wa;
+        }
+
         static_branch_enable(&arch_timer_read_ool_enabled);
 }
 
@@ -369,14 +379,17 @@ static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type t
                 return;
 
         if (needs_unstable_timer_counter_workaround()) {
-                if (wa != timer_unstable_counter_workaround)
+                const struct arch_timer_erratum_workaround *__wa;
+                __wa = __this_cpu_read(timer_unstable_counter_workaround);
+                if (__wa && wa != __wa)
                         pr_warn("Can't enable workaround for %s (clashes with %s\n)",
-                                wa->desc,
-                                timer_unstable_counter_workaround->desc);
-                return;
+                                wa->desc, __wa->desc);
+
+                if (__wa)
+                        return;
         }
 
-        arch_timer_enable_workaround(wa);
+        arch_timer_enable_workaround(wa, local);
         pr_info("Enabling %s workaround for %s\n",
                 local ? "local" : "global", wa->desc);
 }
@@ -384,10 +397,15 @@ static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type t
 #define erratum_handler(fn, r, ...)                                     \
 ({                                                                      \
         bool __val;                                                     \
-        if (needs_unstable_timer_counter_workaround() &&                \
-            timer_unstable_counter_workaround->fn) {                    \
-                r = timer_unstable_counter_workaround->fn(__VA_ARGS__); \
-                __val = true;                                           \
+        if (needs_unstable_timer_counter_workaround()) {                \
+                const struct arch_timer_erratum_workaround *__wa;       \
+                __wa = __this_cpu_read(timer_unstable_counter_workaround); \
+                if (__wa && __wa->fn) {                                 \
+                        r = __wa->fn(__VA_ARGS__);                      \
+                        __val = true;                                   \
+                } else {                                                \
+                        __val = false;                                  \
+                }                                                       \
         } else {                                                        \
                 __val = false;                                          \
         }                                                               \