From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-arm-kernel@lists.infradead.org
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH] arm64/sve: Make kernel FPU protection RT friendly
Date: Thu, 29 Jul 2021 12:52:15 +0200 [thread overview]
Message-ID: <20210729105215.2222338-3-bigeasy@linutronix.de> (raw)
In-Reply-To: <20210729105215.2222338-1-bigeasy@linutronix.de>
Non RT kernels need to protect FPU against preemption and bottom half
processing. This is achieved by disabling bottom halves via
local_bh_disable() which implictly disables preemption.
On RT kernels this protection mechanism is not sufficient because
local_bh_disable() does not disable preemption. It serializes bottom half
related processing via a CPU local lock.
As bottom halves are running always in thread context on RT kernels
disabling preemption is the proper choice as it implicitly prevents bottom
half processing.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/arm64/kernel/fpsimd.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e098f6c67b1de..a208514bd69a9 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -177,10 +177,19 @@ 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();
}
@@ -201,7 +210,10 @@ 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)
--
2.32.0
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next prev parent reply other threads:[~2021-07-29 10:54 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-29 10:52 arm64/sve: Two PREEMPT_RT related arm64 fixes Sebastian Andrzej Siewior
2021-07-29 10:52 ` [PATCH] arm64/sve: Delay freeing memory in fpsimd_flush_thread() Sebastian Andrzej Siewior
2021-07-29 13:58 ` Dave Martin
2021-07-29 14:26 ` Mark Brown
2021-07-29 14:39 ` Sebastian Andrzej Siewior
2021-07-29 15:37 ` Dave Martin
2021-07-29 10:52 ` Sebastian Andrzej Siewior [this message]
2021-07-29 13:54 ` [PATCH] arm64/sve: Make kernel FPU protection RT friendly Dave Martin
2021-07-29 14:17 ` Sebastian Andrzej Siewior
2021-07-29 15:34 ` Dave Martin
2021-07-29 16:00 ` Sebastian Andrzej Siewior
2021-07-29 16:07 ` Sebastian Andrzej Siewior
2021-07-29 16:32 ` Dave Martin
2021-07-29 17:11 ` Sebastian Andrzej Siewior
2021-07-29 14:22 ` Mark Brown
2021-07-29 14:41 ` Sebastian Andrzej Siewior
2021-07-29 16:23 ` Mark Brown
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