From mboxrd@z Thu Jan  1 00:00:00 1970
From: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Subject: Re: [PATCH v2] KVM: MMU: Don't use RCU for lockless shadow walking
Date: Tue, 24 Apr 2012 18:13:37 +0800
Message-ID: <4F967CD1.1020605@linux.vnet.ibm.com>
References: <1335260845-16271-1-git-send-email-avi@redhat.com>
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Cc: Marcelo Tosatti <mtosatti@redhat.com>, kvm@vger.kernel.org
To: Avi Kivity <avi@redhat.com>
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On 04/24/2012 05:47 PM, Avi Kivity wrote:


>  static void kvm_mmu_commit_zap_page(struct kvm *kvm,
>  				    struct list_head *invalid_list)
>  {
> @@ -2021,17 +2006,17 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
>  	if (list_empty(invalid_list))
>  		return;
> 
> -	kvm_flush_remote_tlbs(kvm);
> -
> -	if (atomic_read(&kvm->arch.reader_counter)) {
> -		kvm_mmu_isolate_pages(invalid_list);
> -		sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
> -		list_del_init(invalid_list);
> +	/*
> +	 * wmb: make sure everyone sees our modifications to the page tables


Other lockless vcpu can see a old-copy of a spte, but it is ok since all page
tables is valid to be used. (kvm_flush_remote_tlbs can stop page table to be
freed)

> +	 * rmb: make sure we see changes to vcpu->mode


It is the responsibility of kvm_flush_remote_tlbs to see changes to vcpu->mode.
No?