VisionFive2 Linux kernel

author: Sebastian Andrzej Siewior <bigeasy@linutronix.de> 2021-07-29 10:36:30 +0200 committer: Minda Chen <minda.chen@starfivetech.com> 2023-11-06 19:24:52 +0800 commit: b00b3ea5c737160dd829077636c0f5554e41ef2e parent: dcc75fc8b5cf7334fc212c72538827796803c35a

Commit Summary:

arm64/sve: Make kernel FPU protection RT friendly

Diffstat:

1 file changed, 14 insertions, 2 deletions

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 5e5a869b1f3a..99484e8bbade 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -179,10 +179,19 @@ static void __get_cpu_fpsimd_context(void)
  *
  * The double-underscore version must only be called if you know the task
  * can't be preempted.
+ *
+ * On RT kernels local_bh_disable() is not sufficient because it only
+ * serializes soft interrupt related sections via a local lock, but stays
+ * preemptible. Disabling preemption is the right choice here as bottom
+ * half processing is always in thread context on RT kernels so it
+ * implicitly prevents bottom half processing as well.
  */
 static void get_cpu_fpsimd_context(void)
 {
-	local_bh_disable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_bh_disable();
+	else
+		preempt_disable();
 	__get_cpu_fpsimd_context();
 }
 
@@ -203,7 +212,10 @@ static void __put_cpu_fpsimd_context(void)
 static void put_cpu_fpsimd_context(void)
 {
 	__put_cpu_fpsimd_context();
-	local_bh_enable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_bh_enable();
+	else
+		preempt_enable();
 }
 
 static bool have_cpu_fpsimd_context(void)