failed to load kdump kernel

Steps:
1) In VMWare ESXi create VM with OS Ubuntu 18.04.1 LTS.
2) In Ubuntu compiled and installed Xen 4.11.1~pre.20180911.5acdd26fdc+dfsg-1~exp1
3) Next installed kexec-tools 2.0.16 and kdump-tools 1.6.3-2
4) In /etc/default/grub.d/kdump-tools.cfg change crashkernel value to 512M
5) update-grub
6) reboot

After reboot i try check status: sudo service kdump-tools status
And get:
● kdump-tools.service - Kernel crash dump capture service
   Loaded: loaded (/lib/systemd/system/kdump-tools.service; enabled; vendor preset: enabled)
   Active: active (exited) since Tue 2018-09-25 05:06:10 UTC; 34s ago
  Process: 1046 ExecStart=/etc/init.d/kdump-tools start (code=exited, status=0/SUCCESS)
 Main PID: 1046 (code=exited, status=0/SUCCESS)

сен 25 05:06:09 ptms-all-qa7 systemd[1]: Starting Kernel crash dump capture service...
сен 25 05:06:09 ptms-all-qa7 kdump-tools[1046]: Starting kdump-tools: * Creating symlink /var/lib/kdump/vmlinuz
сен 25 05:06:09 ptms-all-qa7 kdump-tools[1046]: * Creating symlink /var/lib/kdump/initrd.img
сен 25 05:06:09 ptms-all-qa7 kdump-tools[1046]: Memory for crashkernel is not reserved
сен 25 05:06:09 ptms-all-qa7 kdump-tools[1046]: Please reserve memory by passing"crashkernel=X@Y" parameter to kernel
сен 25 05:06:09 ptms-all-qa7 kdump-tools[1046]: Then try to loading kdump kernel
сен 25 05:06:09 ptms-all-qa7 kdump-tools[1046]: * failed to load kdump kernel
сен 25 05:06:10 ptms-all-qa7 kdump-tools[1347]: failed to load kdump kernel
сен 25 05:06:10 ptms-all-qa7 systemd[1]: Started Kernel crash dump capture service.

Log says "Memory for crashkernel is not reserved", but if run: sudo cat /proc/iomem | grep Crash
I get: 18000000-37ffffff : Crash kernel

What to do?