KVM: X86: Optimize zapping rmap

Using rmap_get_first() and rmap_remove() for zapping a huge rmap list could be
slow.  The easy way is to travers the rmap list, collecting the a/d bits and
free the slots along the way.

Provide a pte_list_destroy() and do exactly that.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210730220605.26377-1-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index f1eb2fdfa473d44db2068b2fef410804b6aa4643..232ced2e7bf88b763344fdcb8bf4b815c2914bed 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1007,6 +1007,34 @@ static void pte_list_remove(struct kvm_rmap_head *rmap_head, u64 *sptep)
        __pte_list_remove(sptep, rmap_head);
 }
 
+/* Return true if rmap existed, false otherwise */
+static bool pte_list_destroy(struct kvm_rmap_head *rmap_head)
+{
+       struct pte_list_desc *desc, *next;
+       int i;
+
+       if (!rmap_head->val)
+               return false;
+
+       if (!(rmap_head->val & 1)) {
+               mmu_spte_clear_track_bits((u64 *)rmap_head->val);
+               goto out;
+       }
+
+       desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
+
+       for (; desc; desc = next) {
+               for (i = 0; i < desc->spte_count; i++)
+                       mmu_spte_clear_track_bits(desc->sptes[i]);
+               next = desc->more;
+               mmu_free_pte_list_desc(desc);
+       }
+out:
+       /* rmap_head is meaningless now, remember to reset it */
+       rmap_head->val = 0;
+       return true;
+}
+
 static struct kvm_rmap_head *__gfn_to_rmap(gfn_t gfn, int level,
                                           const struct kvm_memory_slot *slot)
 {
@@ -1398,18 +1426,7 @@ static bool rmap_write_protect(struct kvm_vcpu *vcpu, u64 gfn)
 static bool kvm_zap_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
                          const struct kvm_memory_slot *slot)
 {
-       u64 *sptep;
-       struct rmap_iterator iter;
-       bool flush = false;
-
-       while ((sptep = rmap_get_first(rmap_head, &iter))) {
-               rmap_printk("spte %p %llx.\n", sptep, *sptep);
-
-               pte_list_remove(rmap_head, sptep);
-               flush = true;
-       }
-
-       return flush;
+       return pte_list_destroy(rmap_head);
 }
 
 static bool kvm_unmap_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,