2015-06-11 04:05:39

by Chunyan Zhang

Subject: [PATCH] arm64: fix bug for reloading FPSIMD state after CPU hotplug.

From: Janet Liu <[email protected]>

Now FPSIMD don't handle HOTPLUG_CPU. This introduces bug after cpu down/up process.

After cpu down/up process, the FPSMID hardware register is default value, not any
process's fpsimd context. when CPU_DEAD set cpu's fpsimd_state to NULL, it will force
to load the fpsimd context for the thread, to avoid the chance to skip to load the context.
If process A is the last user process on CPU N before cpu down, and the first user process
on the same CPU N after cpu up, A's fpsimd_state.cpu is the current cpu id,
and per_cpu(fpsimd_last_state) points A's fpsimd_state, so kernel will not reload the
context during it return to user space.

Signed-off-by: Janet Liu <[email protected]>
Signed-off-by: Xiongshan An <[email protected]>
Signed-off-by: Chunyan Zhang <[email protected]>
---
arch/arm64/kernel/fpsimd.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 3dca156..35ef3a2 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -23,6 +23,7 @@
#include <linux/sched.h>
#include <linux/signal.h>
#include <linux/hardirq.h>
+#include <linux/cpu.h>

#include <asm/fpsimd.h>
#include <asm/cputype.h>
@@ -296,6 +297,36 @@ static void fpsimd_pm_init(void)
static inline void fpsimd_pm_init(void) { }
#endif /* CONFIG_CPU_PM */

+#ifdef CONFIG_HOTPLUG_CPU
+static int fpsimd_cpu_hotplug_notifier(struct notifier_block *nfb,
+ unsigned long action,
+ void *hcpu)
+{
+ int cpu = (long)hcpu;
+
+ switch (action & ~CPU_TASKS_FROZEN) {
+ case CPU_DEAD:
+ per_cpu(fpsimd_last_state, cpu) = NULL;
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block fpsimd_cpu_hotplug_notifier_block = {
+ .notifier_call = fpsimd_cpu_hotplug_notifier,
+};
+
+static inline void fpsimd_hotplug_init(void)
+{
+ register_cpu_notifier(&fpsimd_cpu_hotplug_notifier_block);
+}
+
+#else
+static inline void fpsimd_hotplug_init(void) { }
+#endif
+
/*
* FP/SIMD support code initialisation.
*/
@@ -315,6 +346,7 @@ static int __init fpsimd_init(void)
elf_hwcap |= HWCAP_ASIMD;

fpsimd_pm_init();
+ fpsimd_hotplug_init();

return 0;
}
--
1.7.9.5

2015-06-11 16:09:01

by Catalin Marinas

Subject: Re: [PATCH] arm64: fix bug for reloading FPSIMD state after CPU hotplug.

On Thu, Jun 11, 2015 at 12:02:45PM +0800, Chunyan Zhang wrote:
> From: Janet Liu <[email protected]>
>
> Now FPSIMD don't handle HOTPLUG_CPU. This introduces bug after cpu down/up process.
>
> After cpu down/up process, the FPSMID hardware register is default value, not any
> process's fpsimd context. when CPU_DEAD set cpu's fpsimd_state to NULL, it will force
> to load the fpsimd context for the thread, to avoid the chance to skip to load the context.
> If process A is the last user process on CPU N before cpu down, and the first user process
> on the same CPU N after cpu up, A's fpsimd_state.cpu is the current cpu id,
> and per_cpu(fpsimd_last_state) points A's fpsimd_state, so kernel will not reload the
> context during it return to user space.
>
> Signed-off-by: Janet Liu <[email protected]>
> Signed-off-by: Xiongshan An <[email protected]>
> Signed-off-by: Chunyan Zhang <[email protected]>

Applied. Thanks.

--
Catalin