linux-kernel - Re: [PATCH v3] KVM: Check the allocation of pv cpu mask

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Message-ID: <87imbwbyky.fsf@vitty.brq.redhat.com>
Date:   Tue, 29 Sep 2020 13:40:29 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     lihaiwei.kernel@...il.com, linux-kernel@...r.kernel.org
Cc:     pbonzini@...hat.com, sean.j.christopherson@...el.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        Haiwei Li <lihaiwei@...cent.com>, kvm@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v3] KVM: Check the allocation of pv cpu mask

lihaiwei.kernel@...il.com writes:

> From: Haiwei Li <lihaiwei@...cent.com>
>
> check the allocation of per-cpu __pv_cpu_mask.
>
> Suggested-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: Haiwei Li <lihaiwei@...cent.com>
> ---
> v1 -> v2:
>  * add CONFIG_SMP for kvm_send_ipi_mask_allbutself to prevent build error
> v2 -> v3:
>  * always check the allocation of __pv_cpu_mask in kvm_flush_tlb_others
>
>  arch/x86/kernel/kvm.c | 27 ++++++++++++++++++++++++---
>  1 file changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 9663ba31347c..1e5da6db519c 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -553,7 +553,6 @@ static void kvm_send_ipi_mask_allbutself(const struct cpumask *mask, int vector)
>  static void kvm_setup_pv_ipi(void)
>  {
>  	apic->send_IPI_mask = kvm_send_ipi_mask;
> -	apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself;

I see that kvm_send_ipi_mask_allbutself() uses per CPU __pv_cpu_mask and
kvm_send_ipi_mask doesn't but assigning send_IPI_mask here and
send_IPI_mask_allbutself in kvm_alloc_cpumask() looks weird. Personally,
I'd prefet to move apic->send_IPI_mask to kvm_alloc_cpumask() too
(probably call kvm_setup_pv_ipi() and get rid of kvm_apic_init()
completely).

Alternatively, we can save the original apic->send_IPI_mask_allbutself
value to a variable and call it from kvm_send_ipi_mask_allbutself() when
__pv_cpu_mask wasn't allocated.

>  	pr_info("setup PV IPIs\n");
>  }
>  
> @@ -619,6 +618,11 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask,
>  	struct kvm_steal_time *src;
>  	struct cpumask *flushmask = this_cpu_cpumask_var_ptr(__pv_cpu_mask);
>  
> +	if (unlikely(!flushmask)) {
> +		native_flush_tlb_others(cpumask, info);
> +		return;
> +	}
> +
>  	cpumask_copy(flushmask, cpumask);
>  	/*
>  	 * We have to call flush only on online vCPUs. And
> @@ -765,6 +769,14 @@ static __init int activate_jump_labels(void)
>  }
>  arch_initcall(activate_jump_labels);
>  
> +static void kvm_free_cpumask(void)
> +{
> +	unsigned int cpu;
> +
> +	for_each_possible_cpu(cpu)
> +		free_cpumask_var(per_cpu(__pv_cpu_mask, cpu));
> +}
> +
>  static __init int kvm_alloc_cpumask(void)
>  {
>  	int cpu;
> @@ -783,11 +795,20 @@ static __init int kvm_alloc_cpumask(void)
>  
>  	if (alloc)
>  		for_each_possible_cpu(cpu) {
> -			zalloc_cpumask_var_node(per_cpu_ptr(&__pv_cpu_mask, cpu),
> -				GFP_KERNEL, cpu_to_node(cpu));
> +			if (!zalloc_cpumask_var_node(
> +				per_cpu_ptr(&__pv_cpu_mask, cpu),
> +				GFP_KERNEL, cpu_to_node(cpu)))
> +				goto zalloc_cpumask_fail;
>  		}
>  
> +#if defined(CONFIG_SMP)
> +	apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself;
> +#endif
>  	return 0;
> +
> +zalloc_cpumask_fail:
> +	kvm_free_cpumask();
> +	return -ENOMEM;
>  }
>  arch_initcall(kvm_alloc_cpumask);

-- 
Vitaly