Now to gain a good result, lets use 1G Huge Pages.
Kernel cmdline:
  default_hugepagesz=1G hugepagesz=1G hugepages=1210

Gives:
HugePages_Total:    1210
HugePages_Free:     1210
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:    1048576 kB
  
Guest config extra:
 <memoryBacking>
   <hugepages/>
 </memoryBacking>

Slightly changed profile:

Samples: 28K of event 'cycles:ppp', Event count (approx.): 19134377327
Overhead  Shared Object            Symbol
  27.02%  [kernel]                 [k] follow_hugetlb_page
  11.23%  [kernel]                 [k] __get_user_pages
   9.10%  [kernel]                 [k] _raw_spin_lock
   7.58%  [kernel]                 [k] down_read
   7.53%  [kernel]                 [k] up_read
   6.14%  [kernel]                 [k] huge_pte_offset

T4: use 1.2 TB with one PT device, 1G sized explicit HugePages
  #1: 59 seconds
  #2: 21 seconds
  #3: 18 seconds

This is what you'd expect from such a huge guest, and it works just as
expected.

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https://bugs.launchpad.net/bugs/1838575

Title:
  passthrough devices cause >17min boot delay

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