[PATCH] RISC-V: cpu-hotplug fix

[PATCH] RISC-V: cpu-hotplug fix

[Danil Skrebenkov]

openSBI v1.7 adds harts checks for ipi operations. Especially it
adds comparison between hmask passed as an argument from linux
and mask of online harts (from openSBI side). If they don't
fit each other the error occurs.

When cpu is offline, cpu_online_mask is explicitly cleared in
__cpu_disable. However, there is no explicit clearing of
mm_cpumask. mm_cpumask is used for rfence operations that
call openSBI RFENCE extension which uses ipi to remote harts.
If hart is offline there may be error if mask of linux is not
as mask of online harts in openSBI.

this patch adds explicit clearing of mm_cpumask for offline hart.

Signed-off-by: Danil Skrebenkov <danil.skrebenkov@cloudbear.ru>
---
 arch/riscv/kernel/cpu-hotplug.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/kernel/cpu-hotplug.c b/arch/riscv/kernel/cpu-hotplug.c
index a1e38ecfc8be..3f50d3dd76c6 100644
--- a/arch/riscv/kernel/cpu-hotplug.c
+++ b/arch/riscv/kernel/cpu-hotplug.c
@@ -54,6 +54,7 @@ void arch_cpuhp_cleanup_dead_cpu(unsigned int cpu)
 
 	pr_notice("CPU%u: off\n", cpu);
 
+	clear_tasks_mm_cpumask(cpu);
 	/* Verify from the firmware if the cpu is really stopped*/
 	if (cpu_ops->cpu_is_stopped)
 		ret = cpu_ops->cpu_is_stopped(cpu);
-- 
2.43.0

Re: [PATCH] RISC-V: cpu-hotplug fix

[Andrew Jones]

On Fri, Sep 19, 2025 at 04:28:46PM +0300, Danil Skrebenkov wrote:
> openSBI v1.7 adds harts checks for ipi operations. Especially it
> adds comparison between hmask passed as an argument from linux
> and mask of online harts (from openSBI side). If they don't
> fit each other the error occurs.
> 
> When cpu is offline, cpu_online_mask is explicitly cleared in
> __cpu_disable. However, there is no explicit clearing of
> mm_cpumask. mm_cpumask is used for rfence operations that
> call openSBI RFENCE extension which uses ipi to remote harts.
> If hart is offline there may be error if mask of linux is not
> as mask of online harts in openSBI.
> 
> this patch adds explicit clearing of mm_cpumask for offline hart.
> 
> Signed-off-by: Danil Skrebenkov <danil.skrebenkov@cloudbear.ru>
> ---
>  arch/riscv/kernel/cpu-hotplug.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/riscv/kernel/cpu-hotplug.c b/arch/riscv/kernel/cpu-hotplug.c
> index a1e38ecfc8be..3f50d3dd76c6 100644
> --- a/arch/riscv/kernel/cpu-hotplug.c
> +++ b/arch/riscv/kernel/cpu-hotplug.c
> @@ -54,6 +54,7 @@ void arch_cpuhp_cleanup_dead_cpu(unsigned int cpu)
>  
>  	pr_notice("CPU%u: off\n", cpu);
>  
> +	clear_tasks_mm_cpumask(cpu);
>  	/* Verify from the firmware if the cpu is really stopped*/
>  	if (cpu_ops->cpu_is_stopped)
>  		ret = cpu_ops->cpu_is_stopped(cpu);
> -- 
> 2.43.0
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Re: [PATCH] RISC-V: cpu-hotplug fix

[Paul Walmsley]

On Fri, 19 Sep 2025, Danil Skrebenkov wrote:

> openSBI v1.7 adds harts checks for ipi operations. Especially it
> adds comparison between hmask passed as an argument from linux
> and mask of online harts (from openSBI side). If they don't
> fit each other the error occurs.
> 
> When cpu is offline, cpu_online_mask is explicitly cleared in
> __cpu_disable. However, there is no explicit clearing of
> mm_cpumask. mm_cpumask is used for rfence operations that
> call openSBI RFENCE extension which uses ipi to remote harts.
> If hart is offline there may be error if mask of linux is not
> as mask of online harts in openSBI.
> 
> this patch adds explicit clearing of mm_cpumask for offline hart.
> 
> Signed-off-by: Danil Skrebenkov <danil.skrebenkov@cloudbear.ru>

Thanks, queued for early v6.18-rc after cleaning up the subject line to be 
more descriptive:

"RISC-V: clear hot-unplugged cores from all task mm_cpumasks to avoid 
rfence errors"


- Paul