KVM: MMU: split the operations of kvm_mmu_zap_page()

Using kvm_mmu_prepare_zap_page() and kvm_mmu_commit_zap_page() to
split kvm_mmu_zap_page() function, then we can:

- traverse hlist safely
- easily to gather remote tlb flush which occurs during page zapped

Those feature can be used in the later patches

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 43 insertions, 9 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 881ad918455..9b849a70742 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -916,6 +916,7 @@ static int is_empty_shadow_page(u64 *spt)
 static void kvm_mmu_free_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 {
         ASSERT(is_empty_shadow_page(sp->spt));
+        hlist_del(&sp->hash_link);
         list_del(&sp->link);
         __free_page(virt_to_page(sp->spt));
         if (!sp->role.direct)
@@ -1200,6 +1201,10 @@ static void kvm_unlink_unsync_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 }
 
 static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp);
+static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+                                    struct list_head *invalid_list);
+static void kvm_mmu_commit_zap_page(struct kvm *kvm,
+                                    struct list_head *invalid_list);
 
 #define for_each_gfn_sp(kvm, sp, gfn, pos, n)                           \
   hlist_for_each_entry_safe(sp, pos, n,                                 \
@@ -1530,7 +1535,8 @@ static void kvm_mmu_unlink_parents(struct kvm *kvm, struct kvm_mmu_page *sp)
 }
 
 static int mmu_zap_unsync_children(struct kvm *kvm,
-                                   struct kvm_mmu_page *parent)
+                                   struct kvm_mmu_page *parent,
+                                   struct list_head *invalid_list)
 {
         int i, zapped = 0;
         struct mmu_page_path parents;
@@ -1544,7 +1550,7 @@ 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_prepare_zap_page(kvm, sp, invalid_list);
                         mmu_pages_clear_parents(&parents);
                         zapped++;
                 }
@@ -1554,16 +1560,16 @@ 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_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+                                    struct list_head *invalid_list)
 {
         int ret;
 
-        trace_kvm_mmu_zap_page(sp);
+        trace_kvm_mmu_prepare_zap_page(sp);
         ++kvm->stat.mmu_shadow_zapped;
-        ret = mmu_zap_unsync_children(kvm, sp);
+        ret = mmu_zap_unsync_children(kvm, sp, invalid_list);
         kvm_mmu_page_unlink_children(kvm, sp);
         kvm_mmu_unlink_parents(kvm, sp);
-        kvm_flush_remote_tlbs(kvm);
         if (!sp->role.invalid && !sp->role.direct)
                 unaccount_shadowed(kvm, sp->gfn);
         if (sp->unsync)
@@ -1571,17 +1577,45 @@ static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp)
         if (!sp->root_count) {
                 /* Count self */
                 ret++;
-                hlist_del(&sp->hash_link);
-                kvm_mmu_free_page(kvm, sp);
+                list_move(&sp->link, invalid_list);
         } else {
-                sp->role.invalid = 1;
                 list_move(&sp->link, &kvm->arch.active_mmu_pages);
                 kvm_reload_remote_mmus(kvm);
         }
+
+        sp->role.invalid = 1;
         kvm_mmu_reset_last_pte_updated(kvm);
         return ret;
 }
 
+static void kvm_mmu_commit_zap_page(struct kvm *kvm,
+                                    struct list_head *invalid_list)
+{
+        struct kvm_mmu_page *sp;
+
+        if (list_empty(invalid_list))
+                return;
+
+        kvm_flush_remote_tlbs(kvm);
+
+        do {
+                sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
+                WARN_ON(!sp->role.invalid || sp->root_count);
+                kvm_mmu_free_page(kvm, sp);
+        } while (!list_empty(invalid_list));
+
+}
+
+static int kvm_mmu_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp)
+{
+        LIST_HEAD(invalid_list);
+        int ret;
+
+        ret = kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
+        kvm_mmu_commit_zap_page(kvm, &invalid_list);
+        return ret;
+}
+
 /*
  * Changing the number of mmu pages allocated to the vm
  * Note: if kvm_nr_mmu_pages is too small, you will get dead lock