Re: [PATCH 09/10 RFC] KVM: x86: MMU: Move parent_pte handling from kvm_mmu_get_page() to link_shadow_page()

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 11/12/2015 07:56 PM, Takuya Yoshikawa wrote:
> Every time kvm_mmu_get_page() is called with a non-NULL parent_pte
> argument, link_shadow_page() follows that to set the parent entry so
> that the new mapping will point to the returned page table.
>
> Moving parent_pte handling there allows to clean up the code because
> parent_pte is passed to kvm_mmu_get_page() just for mark_unsync() and
> mmu_page_add_parent_pte().
>
> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
> ---
>   arch/x86/kvm/mmu.c         | 21 ++++++++-------------
>   arch/x86/kvm/paging_tmpl.h |  6 ++----
>   2 files changed, 10 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 9273cd4..33fe720 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2108,14 +2108,9 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
>   		if (sp->unsync_children) {
>   			kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
>   			kvm_mmu_mark_parents_unsync(sp);
> -			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);
>
>   		__clear_sp_write_flooding_count(sp);
>   		trace_kvm_mmu_get_page(sp, false);
> @@ -2127,7 +2122,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
>   	sp = kvm_mmu_alloc_page(vcpu, direct);
>
>   	sp->parent_ptes.val = 0;
> -	mmu_page_add_parent_pte(vcpu, sp, parent_pte);
>
>   	sp->gfn = gfn;
>   	sp->role = role;
> @@ -2196,7 +2190,8 @@ static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator)
>   	return __shadow_walk_next(iterator, *iterator->sptep);
>   }
>
> -static void link_shadow_page(u64 *sptep, struct kvm_mmu_page *sp, bool accessed)
> +static void link_shadow_page(struct kvm_vcpu *vcpu, u64 *sptep,
> +			     struct kvm_mmu_page *sp, bool accessed)
>   {
>   	u64 spte;
>
> @@ -2210,6 +2205,11 @@ static void link_shadow_page(u64 *sptep, struct kvm_mmu_page *sp, bool accessed)
>   		spte |= shadow_accessed_mask;
>
>   	mmu_spte_set(sptep, spte);
> +
> +	if (sp->unsync_children || sp->unsync)
> +		mark_unsync(sptep);

Why are these needed?