Subject: Re: [RFC 02/11] powerpc: kvm: ensure vcpu-thread run only on primary hwthread

From: Srikar Dronamraju <[email-masked]>
Date: Wed, 12 Nov 2014 15:47:41 +0530

* [email-masked] <[email-masked]> [2014-10-16 15:29:51]:

> When vcpu thread runs at the first time, it will ensure to stick
> to the primary thread.
> 
> Signed-off-by: Liu Ping Fan <[email-masked]>
> ---
>  arch/powerpc/include/asm/kvm_host.h |  3 +++
>  arch/powerpc/kvm/book3s_hv.c        | 17 +++++++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index 98d9dd5..9a3355e 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -666,6 +666,9 @@ struct kvm_vcpu_arch {
>  	spinlock_t tbacct_lock;
>  	u64 busy_stolen;
>  	u64 busy_preempt;
> +#ifdef CONFIG_KVMPPC_ENABLE_SECONDARY
> +	bool cpu_selected;
> +#endif
>  #endif
>  };
>  
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 27cced9..ba258c8 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1909,6 +1909,23 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
>  {
>  	int r;
>  	int srcu_idx;
> +#ifdef CONFIG_KVMPPC_ENABLE_SECONDARY
> +	int cpu = smp_processor_id();
> +	int target_cpu;
> +	unsigned int cpu;

2 variables with same name... cpu

> +	struct task_struct *p = current;
> +
> +	if (unlikely(!vcpu->arch.cpu_selected)) {
> +		vcpu->arch.cpu_selected = true;

Nit: something like cpumask_set seems to be better than cpu_selected

> +		for (cpu = 0; cpu < NR_CPUS; cpu+=threads_per_core) {
> +			cpumask_set_cpu(cpu, &p->sys_allowed);
		Dont we need to reset the cpumask first before we set
		the cpumask here?

> +		}
> +		if (cpu%threads_per_core != 0) {

At this time, cpu should be NR_CPUS and most times it should be a
multiple of threads_per_core. Unfortunately there wont be a cpu with
cpu number NR_CPUS.

> +			target_cpu = cpu/threads_per_core*threads_per_core;

Its probably better of to have parenthesis here. 

> +			migrate_task_to(current, target_cpu);
We are probably migrating to a non-existant cpu.
Also dont you need to check if the target_cpu is part of the cpumask?

> +		}
> +	}
> +#endif
>  
>  	if (!vcpu->arch.sane) {
>  		run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> -- 
> 1.8.3.1
> 
> 

-- 
Thanks and Regards
Srikar Dronamraju