linux-kernel - Re: [PATCH 10/12] KVM: MMU: allow locklessly access shadow page table out of vcpu thread

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Date:	Wed, 7 Aug 2013 22:09:27 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	gleb@...hat.com, avi.kivity@...il.com, mtosatti@...hat.com,
	pbonzini@...hat.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH 10/12] KVM: MMU: allow locklessly access shadow page
 table out of vcpu thread

On Tue, 30 Jul 2013 21:02:08 +0800
Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com> wrote:

> @@ -2342,6 +2358,13 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
>  	 */
>  	kvm_flush_remote_tlbs(kvm);
>  
> +	if (kvm->arch.rcu_free_shadow_page) {
> +		sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
> +		list_del_init(invalid_list);
> +		call_rcu(&sp->rcu, free_pages_rcu);
> +		return;
> +	}
> +
>  	list_for_each_entry_safe(sp, nsp, invalid_list, link) {
>  		WARN_ON(!sp->role.invalid || sp->root_count);
>  		kvm_mmu_free_page(sp);

Shouldn't we avoid calling call_rcu() when we are holding mmu_lock?

	Takuya
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