virtualbox.org

HOST:win10 x64
vbox version:5.1.26
1. install win10x64 as guest on UEFI mode

2. then install deepin linux , thus two OS were in one guest

3.install refind loader in windows(copy the file to esp dir,and edit bcd)

4.restart windows by the button of windows OS(not button of vbox), yes, the guest restar to the refind menu, but,shut down the guest and close vbox and then start open vbox start guest ,it will show the grub menu ,,i have to re-edit the bcd file toshow the refind menu !

If you ask yourself "where does rEFIND settings are saved", you'll have the answer.
Hint; no, there's no virtual EPROM where these settings are saved.

my English isn good,you mean refind menu setting saved at at physical hardware called "EPROM " which vbox can not simulate? I just think it read the "refind.conf" file each time to load the menu when vbox start, before asking this.
Ps:Incase misunderstanding my question,i re-description it as "why do I have edit the refind.conf file to show windows and linux selection menu successful first time but faild to show them after restarted vbox?"

You cannot save the EFI settings. EFI support is experimental.