Re: [PATCH] kvm x86 mmu: simplify kvm_mmu_unlink_parents()

[Marcelo Tosatti <mtosatti@redhat.com>]

On Sat, Apr 17, 2010 at 04:50:13PM +0800, Lai Jiangshan wrote:
> 
> mmu_page_remove_parent_pte() does much maintenance works,
> but kvm_mmu_unlink_parents() unlink all parents, so
> such maintenance works are not need.
> 
> This patch simplifies the works of kvm_mmu_unlink_parents()
> by unlinking parents without so many maintenance works.
> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 90f666e..71faa04 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1453,22 +1453,33 @@ static void kvm_mmu_reset_last_pte_updated(struct kvm *kvm)
>  
>  static void kvm_mmu_unlink_parents(struct kvm *kvm, struct kvm_mmu_page *sp)
>  {
> -	u64 *parent_pte;
> +	if (!sp->multimapped) {
> +		if (!sp->parent_pte)
> +			return;
>  
> -	while (sp->multimapped || sp->parent_pte) {
> -		if (!sp->multimapped)
> -			parent_pte = sp->parent_pte;
> -		else {
> -			struct kvm_pte_chain *chain;
> +		__set_spte(sp->parent_pte, shadow_trap_nonpresent_pte);
> +		sp->parent_pte = NULL;
> +		return;
> +	}
>  
> -			chain = container_of(sp->parent_ptes.first,
> -					     struct kvm_pte_chain, link);
> -			parent_pte = chain->parent_ptes[0];
> +	while (!hlist_empty(&sp->parent_ptes)) {
> +		struct kvm_pte_chain *chain;
> +		u64 *parent_pte;
> +		int i;
> +
> +		chain = hlist_entry(sp->parent_ptes.first,
> +				    struct kvm_pte_chain, link);
> +		for (i = 0; i < NR_PTE_CHAIN_ENTRIES; ++i) {
> +			parent_pte = chain->parent_ptes[i];
> +			if (!parent_pte)
> +				break;
> +			__set_spte(parent_pte, shadow_trap_nonpresent_pte);
>  		}
> -		BUG_ON(!parent_pte);
> -		kvm_mmu_put_page(sp, parent_pte);
> -		__set_spte(parent_pte, shadow_trap_nonpresent_pte);
> +		hlist_del(&chain->link);
> +		mmu_free_pte_chain(chain);
>  	}
> +	sp->multimapped = 0;
> +	sp->parent_pte = NULL;
>  }
>  
>  static int mmu_zap_unsync_children(struct kvm *kvm,
> 

Personally i don't see why this is any better than the previous code.