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Re: [PATCH] sched: move vCPU exec state barriers
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 6 Feb 2026 16:02:07 +0100
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- Cc: Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, George Dunlap <gwd@xxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 06 Feb 2026 15:02:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06.02.2026 13:57, Oleksii Kurochko wrote:
>
> On 2/5/26 12:33 PM, Jan Beulich wrote:
>> The barrier in vcpu_context_saved() is specifically about the clearing of
>> ->is_running. It isn't needed when we don't clear the flag.
>>
>> Furthermore, one side of the barrier being in common code, the other would
>> better be, too. This way, all architectures are covered (beyond any
>> specific needs they may have).
>
> Don't we want then move ...
>
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> --- a/xen/arch/arm/domain.c
>> +++ b/xen/arch/arm/domain.c
>> @@ -333,17 +333,7 @@ void sync_local_execstate(void)
>>
>> void sync_vcpu_execstate(struct vcpu *v)
>> {
>> - /*
>> - * We don't support lazy switching.
>> - *
>> - * However the context may have been saved from a remote pCPU so we
>> - * need a barrier to ensure it is observed before continuing.
>> - *
>> - * Per vcpu_context_saved(), the context can be observed when
>> - * v->is_running is false (the caller should check it before calling
>> - * this function).
>> - */
>> - smp_rmb();
>> + /* Nothing to do -- no lazy switching */
>> }
>
> ... to common code with ability to re-define sync_vcpu_execstate() by arch
> as only x86 does something inside this function?
Indeed this was considered already, as a possible next step.
Jan
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