Re: [PATCH 08/11] KVM: MMU: use page track for non-leaf shadow pages

[Kai Huang <kai.huang@linux.intel.com>]

On 12/01/2015 02:26 AM, Xiao Guangrong wrote:
> non-leaf shadow pages are always write protected, it can be the user
> of page track
>
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> ---
>   arch/x86/include/asm/kvm_page_track.h |  8 +++++
>   arch/x86/kvm/mmu.c                    | 26 +++++++++++++---
>   arch/x86/kvm/page_track.c             | 58 +++++++++++++++++++++++------------
>   3 files changed, 67 insertions(+), 25 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
> index 6744234..3447dac 100644
> --- a/arch/x86/include/asm/kvm_page_track.h
> +++ b/arch/x86/include/asm/kvm_page_track.h
> @@ -41,8 +41,16 @@ int kvm_page_track_create_memslot(struct kvm_memory_slot *slot,
>   void kvm_page_track_free_memslot(struct kvm_memory_slot *free,
>   				 struct kvm_memory_slot *dont);
>   
> +void
> +kvm_slot_page_track_add_page_nolock(struct kvm *kvm,
> +				    struct kvm_memory_slot *slot, gfn_t gfn,
> +				    enum kvm_page_track_mode mode);
>   void kvm_page_track_add_page(struct kvm *kvm, gfn_t gfn,
>   			     enum kvm_page_track_mode mode);
> +void kvm_slot_page_track_remove_page_nolock(struct kvm *kvm,
> +					    struct kvm_memory_slot *slot,
> +					    gfn_t gfn,
> +					    enum kvm_page_track_mode mode);
>   void kvm_page_track_remove_page(struct kvm *kvm, gfn_t gfn,
>   				enum kvm_page_track_mode mode);
>   bool kvm_page_track_check_mode(struct kvm_vcpu *vcpu, gfn_t gfn,
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index b23f9fc..5a2ca73 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -806,11 +806,17 @@ static void account_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
>   	struct kvm_memory_slot *slot;
>   	gfn_t gfn;
>   
> +	kvm->arch.indirect_shadow_pages++;
>   	gfn = sp->gfn;
>   	slots = kvm_memslots_for_spte_role(kvm, sp->role);
>   	slot = __gfn_to_memslot(slots, gfn);
> +
> +	/* the non-leaf shadow pages are keeping readonly. */
> +	if (sp->role.level > PT_PAGE_TABLE_LEVEL)
> +		return kvm_slot_page_track_add_page_nolock(kvm, slot, gfn,
> +							KVM_PAGE_TRACK_WRITE);
> +
>   	kvm_mmu_gfn_disallow_lpage(slot, gfn);
> -	kvm->arch.indirect_shadow_pages++;
>   }
>   
>   static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
> @@ -819,11 +825,15 @@ static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
>   	struct kvm_memory_slot *slot;
>   	gfn_t gfn;
>   
> +	kvm->arch.indirect_shadow_pages--;
>   	gfn = sp->gfn;
>   	slots = kvm_memslots_for_spte_role(kvm, sp->role);
>   	slot = __gfn_to_memslot(slots, gfn);
> +	if (sp->role.level > PT_PAGE_TABLE_LEVEL)
> +		return kvm_slot_page_track_remove_page_nolock(kvm, slot, gfn,
> +							KVM_PAGE_TRACK_WRITE);
> +
>   	kvm_mmu_gfn_allow_lpage(slot, gfn);
> -	kvm->arch.indirect_shadow_pages--;
>   }
>   
>   static bool __mmu_gfn_lpage_is_disallowed(gfn_t gfn, int level,
> @@ -2140,12 +2150,18 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
>   	hlist_add_head(&sp->hash_link,
>   		&vcpu->kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)]);
>   	if (!direct) {
> -		if (rmap_write_protect(vcpu, gfn))
> +		/*
> +		 * we should do write protection before syncing pages
> +		 * otherwise the content of the synced shadow page may
> +		 * be inconsistent with guest page table.
> +		 */
> +		account_shadowed(vcpu->kvm, sp);
> +
> +		if (level == PT_PAGE_TABLE_LEVEL &&
> +		      rmap_write_protect(vcpu, gfn))
>   			kvm_flush_remote_tlbs(vcpu->kvm);
I think your modification is good but I am little bit confused here. In 
account_shadowed, if sp->role.level > PT_PAGE_TABLE_LEVEL, the sp->gfn 
is write protected, and this is reasonable. So why write protecting the 
gfn of PT_PAGE_TABLE_LEVEL here?

>   		if (level > PT_PAGE_TABLE_LEVEL && need_sync)
>   			kvm_sync_pages(vcpu, gfn);
> -
> -		account_shadowed(vcpu->kvm, sp);
>   	}
>   	sp->mmu_valid_gen = vcpu->kvm->arch.mmu_valid_gen;
>   	init_shadow_page_table(sp);
> diff --git a/arch/x86/kvm/page_track.c b/arch/x86/kvm/page_track.c
> index 84420df..87554d3 100644
> --- a/arch/x86/kvm/page_track.c
> +++ b/arch/x86/kvm/page_track.c
> @@ -77,6 +77,26 @@ static void update_gfn_track(struct kvm_memory_slot *slot, gfn_t gfn,
>   	WARN_ON(val < 0);
>   }
>   
> +void
> +kvm_slot_page_track_add_page_nolock(struct kvm *kvm,
> +				    struct kvm_memory_slot *slot, gfn_t gfn,
> +				    enum kvm_page_track_mode mode)
> +{
> +	WARN_ON(!check_mode(mode));
> +
> +	update_gfn_track(slot, gfn, mode, 1);
> +
> +	/*
> +	 * new track stops large page mapping for the
> +	 * tracked page.
> +	 */
> +	kvm_mmu_gfn_disallow_lpage(slot, gfn);
> +
> +	if (mode == KVM_PAGE_TRACK_WRITE)
> +		if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn))
> +			kvm_flush_remote_tlbs(kvm);
> +}
> +
>   /*
>    * add guest page to the tracking pool so that corresponding access on that
>    * page will be intercepted.
> @@ -101,21 +121,27 @@ void kvm_page_track_add_page(struct kvm *kvm, gfn_t gfn,
>   		slot = __gfn_to_memslot(slots, gfn);
>   
>   		spin_lock(&kvm->mmu_lock);
> -		update_gfn_track(slot, gfn, mode, 1);
> -
> -		/*
> -		 * new track stops large page mapping for the
> -		 * tracked page.
> -		 */
> -		kvm_mmu_gfn_disallow_lpage(slot, gfn);
> -
> -		if (mode == KVM_PAGE_TRACK_WRITE)
> -			if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn))
> -				kvm_flush_remote_tlbs(kvm);
> +		kvm_slot_page_track_add_page_nolock(kvm, slot, gfn, mode);
>   		spin_unlock(&kvm->mmu_lock);
>   	}
>   }
>   
> +void kvm_slot_page_track_remove_page_nolock(struct kvm *kvm,
> +					    struct kvm_memory_slot *slot,
> +					    gfn_t gfn,
> +					    enum kvm_page_track_mode mode)
> +{
> +	WARN_ON(!check_mode(mode));
> +
> +	update_gfn_track(slot, gfn, mode, -1);
> +
> +	/*
> +	 * allow large page mapping for the tracked page
> +	 * after the tracker is gone.
> +	 */
> +	kvm_mmu_gfn_allow_lpage(slot, gfn);
> +}
> +
>   /*
>    * remove the guest page from the tracking pool which stops the interception
>    * of corresponding access on that page. It is the opposed operation of
> @@ -134,20 +160,12 @@ void kvm_page_track_remove_page(struct kvm *kvm, gfn_t gfn,
>   	struct kvm_memory_slot *slot;
>   	int i;
>   
> -	WARN_ON(!check_mode(mode));
> -
>   	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
>   		slots = __kvm_memslots(kvm, i);
>   		slot = __gfn_to_memslot(slots, gfn);
>   
>   		spin_lock(&kvm->mmu_lock);
> -		update_gfn_track(slot, gfn, mode, -1);
> -
> -		/*
> -		 * allow large page mapping for the tracked page
> -		 * after the tracker is gone.
> -		 */
> -		kvm_mmu_gfn_allow_lpage(slot, gfn);
> +		kvm_slot_page_track_remove_page_nolock(kvm, slot, gfn, mode);
Looks you need to merge this part with patch 1, as you are modifying 
kvm_page_track_{add,remove}_page here, which are introduced in your patch 1.

Thanks,
-Kai
>   		spin_unlock(&kvm->mmu_lock);
>   	}
>   }