linux-kernel - Re: [PATCH 08/10] KVM: x86: MMU: Use for_each_rmap_spte macro instead of pte_list

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Message-ID: <5655E1DD.9000501@redhat.com>
Date:	Wed, 25 Nov 2015 17:29:17 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	mtosatti@...hat.com, guangrong.xiao@...ux.intel.com
Subject: Re: [PATCH 08/10] KVM: x86: MMU: Use for_each_rmap_spte macro instead
 of pte_list_walk()



On 20/11/2015 09:47, Takuya Yoshikawa wrote:
> kvm_mmu_mark_parents_unsync() alone uses pte_list_walk(), witch does
> nearly the same as the for_each_rmap_spte macro.  The only difference
> is that is_shadow_present_pte() checks cannot be placed there because
> kvm_mmu_mark_parents_unsync() can be called with a new parent pointer
> whose entry is not set yet.
> 
> By calling mark_unsync() separately for the parent and adding the parent
> pointer to the parent_ptes chain later in kvm_mmu_get_page(), the macro
> works with no problem.
> 
> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
> ---
>  arch/x86/kvm/mmu.c | 36 +++++++++++++-----------------------
>  1 file changed, 13 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 7f46e3e..4e29d9a 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1007,26 +1007,6 @@ static void pte_list_remove(u64 *spte, struct kvm_rmap_head *rmap_head)
>  	}
>  }
>  
> -typedef void (*pte_list_walk_fn) (u64 *spte);
> -static void pte_list_walk(struct kvm_rmap_head *rmap_head, pte_list_walk_fn fn)
> -{
> -	struct pte_list_desc *desc;
> -	int i;
> -
> -	if (!rmap_head->val)
> -		return;
> -
> -	if (!(rmap_head->val & 1))
> -		return fn((u64 *)rmap_head->val);
> -
> -	desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
> -	while (desc) {
> -		for (i = 0; i < PTE_LIST_EXT && desc->sptes[i]; ++i)
> -			fn(desc->sptes[i]);
> -		desc = desc->more;
> -	}
> -}
> -
>  static struct kvm_rmap_head *__gfn_to_rmap(gfn_t gfn, int level,
>  					   struct kvm_memory_slot *slot)
>  {
> @@ -1749,7 +1729,12 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu, int direct
>  static void mark_unsync(u64 *spte);
>  static void kvm_mmu_mark_parents_unsync(struct kvm_mmu_page *sp)
>  {
> -	pte_list_walk(&sp->parent_ptes, mark_unsync);
> +	u64 *sptep;
> +	struct rmap_iterator iter;
> +
> +	for_each_rmap_spte(&sp->parent_ptes, &iter, sptep) {
> +		mark_unsync(sptep);
> +	}
>  }
>  
>  static void mark_unsync(u64 *spte)
> @@ -2119,12 +2104,17 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
>  		if (sp->unsync && kvm_sync_page_transient(vcpu, sp))
>  			break;
>  
> -		mmu_page_add_parent_pte(vcpu, sp, parent_pte);
>  		if (sp->unsync_children) {
>  			kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
>  			kvm_mmu_mark_parents_unsync(sp);
> -		} else if (sp->unsync)
> +			if (parent_pte)
> +				mark_unsync(parent_pte);
> +		} else if (sp->unsync) {
>  			kvm_mmu_mark_parents_unsync(sp);
> +			if (parent_pte)
> +				mark_unsync(parent_pte);
> +		}
> +		mmu_page_add_parent_pte(vcpu, sp, parent_pte);

This patch is okay with Xiao's suggestion to remove the
kvm_mmu_mark_parents_unsync call.

Paolo

>  		__clear_sp_write_flooding_count(sp);
>  		trace_kvm_mmu_get_page(sp, false);
> 
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