KVM: reuse memslot in kvm_write_guest_page

Caching memslot value and using mark_page_dirty_in_slot() avoids another
O(log N) search when dirtying the page.
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Message-Id: <1428695247-27603-1-git-send-email-rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -1590,15 +1590,17 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn, const void *data,
 			 int offset, int len)
 {
 	int r;
+	struct kvm_memory_slot *memslot;
 	unsigned long addr;
 
-	addr = gfn_to_hva(kvm, gfn);
+	memslot = gfn_to_memslot(kvm, gfn);
+	addr = gfn_to_hva_memslot(memslot, gfn);
 	if (kvm_is_error_hva(addr))
 		return -EFAULT;
 	r = __copy_to_user((void __user *)addr + offset, data, len);
 	if (r)
 		return -EFAULT;
-	mark_page_dirty(kvm, gfn);
+	mark_page_dirty_in_slot(kvm, memslot, gfn);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(kvm_write_guest_page);