linux-kernel - Re: [PATCH v6 2/7] KVM: MMU: delete shadow page from hash list in kvm_mmu_prepare_zap

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Message-ID: <20130519104713.GE4725@redhat.com>
Date:	Sun, 19 May 2013 13:47:13 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	avi.kivity@...il.com, mtosatti@...hat.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v6 2/7] KVM: MMU: delete shadow page from hash list in
 kvm_mmu_prepare_zap_page

On Fri, May 17, 2013 at 05:12:57AM +0800, Xiao Guangrong wrote:
> Move deletion shadow page from the hash list from kvm_mmu_commit_zap_page to
> kvm_mmu_prepare_zap_page so that we can call kvm_mmu_commit_zap_page
> once for multiple kvm_mmu_prepare_zap_page that can help us to avoid
> unnecessary TLB flush
> 
Don't we call kvm_mmu_commit_zap_page() once for multiple
kvm_mmu_prepare_zap_page() now when possible? kvm_mmu_commit_zap_page()
gets a list as a parameter. I am not against the change, but wish to
understand it better.

> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> ---
>  arch/x86/kvm/mmu.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 40d7b2d..682ecb4 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1466,7 +1466,7 @@ static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, int nr)
>  static void kvm_mmu_free_page(struct kvm_mmu_page *sp)
>  {
>  	ASSERT(is_empty_shadow_page(sp->spt));
> -	hlist_del(&sp->hash_link);
> +
>  	list_del(&sp->link);
>  	free_page((unsigned long)sp->spt);
>  	if (!sp->role.direct)
> @@ -1655,7 +1655,8 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
>  
>  #define for_each_gfn_indirect_valid_sp(_kvm, _sp, _gfn)			\
>  	for_each_gfn_sp(_kvm, _sp, _gfn)				\
> -		if ((_sp)->role.direct || (_sp)->role.invalid) {} else
> +		if ((_sp)->role.direct ||				\
> +		      ((_sp)->role.invalid && WARN_ON(1))) {} else
>  
>  /* @sp->gfn should be write-protected at the call site */
>  static int __kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> @@ -2074,6 +2075,9 @@ static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
>  		unaccount_shadowed(kvm, sp->gfn);
>  	if (sp->unsync)
>  		kvm_unlink_unsync_page(kvm, sp);
> +
> +	hlist_del_init(&sp->hash_link);
> +
What about moving this inside if() bellow and making it hlist_del()?
Leave the page on the hash if root_count is non zero.

>  	if (!sp->root_count) {
>  		/* Count self */
>  		ret++;
> -- 
> 1.7.7.6

--
			Gleb.
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