Re: [PATCH 1/3 v2] KVM MMU: make kvm_mmu_zap_page() return the number of zapped sp in total.

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

Marcelo Tosatti wrote:
> On Fri, Apr 23, 2010 at 01:58:22PM +0800, Gui Jianfeng wrote:
>> Currently, in kvm_mmu_change_mmu_pages(kvm, page), "used_pages--" is  performed after calling
>> kvm_mmu_zap_page() in spite of that whether "page" is actually reclaimed. Because root sp won't 
>> be reclaimed by kvm_mmu_zap_page(). So making kvm_mmu_zap_page() return total number of reclaimed 
>> sp makes more sense. A new flag is put into kvm_mmu_zap_page() to indicate whether the top page is
>> reclaimed.
>>
>> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
>> ---
>>  arch/x86/kvm/mmu.c |   53 +++++++++++++++++++++++++++++++++++----------------
>>  1 files changed, 36 insertions(+), 17 deletions(-)
> 
> Gui, 
> 
> There will be only a few pinned roots, and there is no need for
> kvm_mmu_change_mmu_pages to be precise at that level (pages will be
> reclaimed through kvm_unmap_hva eventually).

Hi Marcelo

Actually, it doesn't only affect kvm_mmu_change_mmu_pages() but also affects kvm_mmu_remove_some_alloc_mmu_pages()
which is called by mmu shrink routine. This will induce upper layer get a wrong number, so i think this should be
fixed. Here is a updated version.

---
From: Gui Jianfeng <guijianfeng@cn.fujitsu.com>

Currently, in kvm_mmu_change_mmu_pages(kvm, page), "used_pages--" is  performed after calling
kvm_mmu_zap_page() in spite of that whether "page" is actually reclaimed. Because root sp won't 
be reclaimed by kvm_mmu_zap_page(). So making kvm_mmu_zap_page() return total number of reclaimed 
sp makes more sense. A new flag is put into kvm_mmu_zap_page() to indicate whether the top page is
reclaimed. kvm_mmu_remove_some_alloc_mmu_pages() also rely on kvm_mmu_zap_page() to return a total
relcaimed number.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
---
 arch/x86/kvm/mmu.c |   53 +++++++++++++++++++++++++++++++++++----------------
 1 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 51eb6d6..e545da8 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1194,12 +1194,13 @@ static void kvm_unlink_unsync_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 	--kvm->stat.mmu_unsync;
 }
 
-static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp);
+static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+			    int *self_deleted);
 
 static int kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 {
 	if (sp->role.cr4_pae != !!is_pae(vcpu)) {
-		kvm_mmu_zap_page(vcpu->kvm, sp);
+		kvm_mmu_zap_page(vcpu->kvm, sp, NULL);
 		return 1;
 	}
 
@@ -1207,7 +1208,7 @@ static int kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 		kvm_flush_remote_tlbs(vcpu->kvm);
 	kvm_unlink_unsync_page(vcpu->kvm, sp);
 	if (vcpu->arch.mmu.sync_page(vcpu, sp)) {
-		kvm_mmu_zap_page(vcpu->kvm, sp);
+		kvm_mmu_zap_page(vcpu->kvm, sp, NULL);
 		return 1;
 	}
 
@@ -1478,7 +1479,7 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
 		struct kvm_mmu_page *sp;
 
 		for_each_sp(pages, sp, parents, i) {
-			kvm_mmu_zap_page(kvm, sp);
+			kvm_mmu_zap_page(kvm, sp, NULL);
 			mmu_pages_clear_parents(&parents);
 			zapped++;
 		}
@@ -1488,7 +1489,8 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
 	return zapped;
 }
 
-static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp)
+static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+			    int *self_deleted)
 {
 	int ret;
 
@@ -1505,11 +1507,16 @@ static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 	if (!sp->root_count) {
 		hlist_del(&sp->hash_link);
 		kvm_mmu_free_page(kvm, sp);
+		/* Count self */
+		ret++;
+		if (self_deleted)
+			*self_deleted = 1;
 	} else {
 		sp->role.invalid = 1;
 		list_move(&sp->link, &kvm->arch.active_mmu_pages);
 		kvm_reload_remote_mmus(kvm);
 	}
+
 	kvm_mmu_reset_last_pte_updated(kvm);
 	return ret;
 }
@@ -1538,8 +1545,7 @@ void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages)
 
 			page = container_of(kvm->arch.active_mmu_pages.prev,
 					    struct kvm_mmu_page, link);
-			used_pages -= kvm_mmu_zap_page(kvm, page);
-			used_pages--;
+			used_pages -= kvm_mmu_zap_page(kvm, page, NULL);
 		}
 		kvm_nr_mmu_pages = used_pages;
 		kvm->arch.n_free_mmu_pages = 0;
@@ -1558,6 +1564,8 @@ static int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)
 	struct kvm_mmu_page *sp;
 	struct hlist_node *node, *n;
 	int r;
+	int self_deleted = 0;
+	int ret;
 
 	pgprintk("%s: looking for gfn %lx\n", __func__, gfn);
 	r = 0;
@@ -1569,7 +1577,8 @@ restart:
 			pgprintk("%s: gfn %lx role %x\n", __func__, gfn,
 				 sp->role.word);
 			r = 1;
-			if (kvm_mmu_zap_page(kvm, sp))
+			ret = kvm_mmu_zap_page(kvm, sp, &self_deleted);
+			if (ret > 1 || (ret == 1 && self_deleted == 0))
 				goto restart;
 		}
 	return r;
@@ -1581,6 +1590,8 @@ static void mmu_unshadow(struct kvm *kvm, gfn_t gfn)
 	struct hlist_head *bucket;
 	struct kvm_mmu_page *sp;
 	struct hlist_node *node, *nn;
+	int ret;
+	int self_deleted = 0;
 
 	index = kvm_page_table_hashfn(gfn);
 	bucket = &kvm->arch.mmu_page_hash[index];
@@ -1590,7 +1601,8 @@ restart:
 		    && !sp->role.invalid) {
 			pgprintk("%s: zap %lx %x\n",
 				 __func__, gfn, sp->role.word);
-			if (kvm_mmu_zap_page(kvm, sp))
+			ret = kvm_mmu_zap_page(kvm, sp, &self_deleted);
+			if (ret > 1 || (ret == 1 && self_deleted == 0))
 				goto restart;
 		}
 	}
@@ -2012,7 +2024,7 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 		sp = page_header(root);
 		--sp->root_count;
 		if (!sp->root_count && sp->role.invalid)
-			kvm_mmu_zap_page(vcpu->kvm, sp);
+			kvm_mmu_zap_page(vcpu->kvm, sp, NULL);
 		vcpu->arch.mmu.root_hpa = INVALID_PAGE;
 		spin_unlock(&vcpu->kvm->mmu_lock);
 		return;
@@ -2025,7 +2037,7 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 			sp = page_header(root);
 			--sp->root_count;
 			if (!sp->root_count && sp->role.invalid)
-				kvm_mmu_zap_page(vcpu->kvm, sp);
+				kvm_mmu_zap_page(vcpu->kvm, sp, NULL);
 		}
 		vcpu->arch.mmu.pae_root[i] = INVALID_PAGE;
 	}
@@ -2604,6 +2616,8 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 	int npte;
 	int r;
 	int invlpg_counter;
+	int ret;
+	int self_deleted = 0;
 
 	pgprintk("%s: gpa %llx bytes %d\n", __func__, gpa, bytes);
 
@@ -2682,7 +2696,9 @@ restart:
 			 */
 			pgprintk("misaligned: gpa %llx bytes %d role %x\n",
 				 gpa, bytes, sp->role.word);
-			if (kvm_mmu_zap_page(vcpu->kvm, sp))
+
+			ret = kvm_mmu_zap_page(vcpu->kvm, sp, &self_deleted);
+			if (ret > 1 || (ret == 1 && self_deleted == 0))
 				goto restart;
 			++vcpu->kvm->stat.mmu_flooded;
 			continue;
@@ -2750,7 +2766,7 @@ void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu)
 
 		sp = container_of(vcpu->kvm->arch.active_mmu_pages.prev,
 				  struct kvm_mmu_page, link);
-		kvm_mmu_zap_page(vcpu->kvm, sp);
+		kvm_mmu_zap_page(vcpu->kvm, sp, NULL);
 		++vcpu->kvm->stat.mmu_recycled;
 	}
 }
@@ -2890,13 +2906,16 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
 void kvm_mmu_zap_all(struct kvm *kvm)
 {
 	struct kvm_mmu_page *sp, *node;
+	int ret;
+	int self_deleted = 0;
 
 	spin_lock(&kvm->mmu_lock);
 restart:
-	list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link)
-		if (kvm_mmu_zap_page(kvm, sp))
+	list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) {
+		ret = kvm_mmu_zap_page(kvm, sp, &self_deleted);
+		if (ret > 1 || (ret == 1 && self_deleted == 0))
 			goto restart;
-
+	}
 	spin_unlock(&kvm->mmu_lock);
 
 	kvm_flush_remote_tlbs(kvm);
@@ -2908,7 +2927,7 @@ static int kvm_mmu_remove_some_alloc_mmu_pages(struct kvm *kvm)
 
 	page = container_of(kvm->arch.active_mmu_pages.prev,
 			    struct kvm_mmu_page, link);
-	return kvm_mmu_zap_page(kvm, page) + 1;
+	return kvm_mmu_zap_page(kvm, page, NULL);
 }
 
 static int mmu_shrink(int nr_to_scan, gfp_t gfp_mask)
-- 
1.6.5.2