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

[decui_microsoft.com (Dexuan Cui)]

decui_microsoft.com added inline comments.

INLINE COMMENTS

> kib wrote in copy.c:79-84
> 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.

@kib  
Got it. Thanks a lot for sharing the details about the background!  Yeah, I've realized the complexity of booting from arbitrary address, which would require a lot of really in-depth and long term work.  So I'd like to use this patch as a temporary workaround for UEFI VM on Hyper-V. :-)

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

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