KVM: introduce a table to map slot id to index in memslots array

The operation of getting dirty log is frequent when framebuffer-based
displays are used(for example, Xwindow), so, we introduce a mapping table
to speed up id_to_memslot()

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 7 insertions, 6 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9efdf5c703a5..8c5c30361b0d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -239,6 +239,8 @@ struct kvm_irq_routing_table {};
 struct kvm_memslots {
         u64 generation;
         struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
+        /* The mapping table from slot id to the index in memslots[]. */
+        int id_to_index[KVM_MEM_SLOTS_NUM];
 };
 
 struct kvm {
@@ -341,14 +343,13 @@ static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
 static inline struct kvm_memory_slot *
 id_to_memslot(struct kvm_memslots *slots, int id)
 {
-        int i;
+        int index = slots->id_to_index[id];
+        struct kvm_memory_slot *slot;
 
-        for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
-                if (slots->memslots[i].id == id)
-                        return &slots->memslots[i];
+        slot = &slots->memslots[index];
 
-        WARN_ON(1);
-        return NULL;
+        WARN_ON(slot->id != id);
+        return slot;
 }
 
 #define HPA_MSB ((sizeof(hpa_t) * 8) - 1)