[Differential] D9686: fix UEFI VM's bootup on Hyper-V (i.e. Hyper-V Generation-2 VM)

[kib (Konstantin Belousov)]

kib added inline comments.

INLINE COMMENTS

> decui_microsoft.com wrote in copy.c:79-84
> IIRC, the UEFI firmware enables protected mode with identity-mapped paging (i.e. VA==PA) , before the execution is transferred to FreeBSD's EFI loader. So here IMO I can treat VA==PA in the patch (it looks FreeBSD UEFI loader doesn't change the VA/PA mapping(?)).
> 
> I have to admit the fact that I don't know the loader very well and actually it's my first time to have the chance to read some of the code and try to make a patch for it. :-)
> 
> Please kindly elaborate a little more about the issues that you think exist in the patch and I am happy to dig more into them.

UEFI firmware is guaranteed to be executed with VA==PA indeed, but loader changes the mapping after ExitBootServices(), making each 2G VA mapped by low 2G physical.

I did not wrote anything about issues in your patch, rather, I tried to enumerate problems that must be handled to allow boot from arbitrary UEFI memory map.

REVISION DETAIL
  https://reviews.freebsd.org/D9686

EMAIL PREFERENCES
  https://reviews.freebsd.org/settings/panel/emailpreferences/

To: decui_microsoft.com, imp, jhb, will, kib, delphij, emaste, sepherosa_gmail.com, honzhan_microsoft.com, howard0su_gmail.com, marcel
Cc: freebsd-virtualization-list