[Bug 246321] Key press timing/repeat issue on UEFI VNC console for OpenBSD => 6.6 guest

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246321

--- Comment #4 from commit-hook at freebsd.org ---
A commit references this bug:

Author: grehan
Date: Thu May 14 22:18:12 UTC 2020
New revision: 361064
URL: https://svnweb.freebsd.org/changeset/base/361064

Log:
  Hide host CPUID 0x15 TSC/Crystal ratio/freq info from guest

  In recent Linux (5.3+) and OpenBSD (6.6+) kernels, and with hosts that
  support CPUID 0x15, the local APIC frequency is determined directly
  from the reported crystal clock to avoid calibration against the 8254
  timer.

  However, the local APIC frequency implemented by bhyve is 128MHz, where
  most h/w systems report frequencies around 25MHz. This shows up on
  OpenBSD guests as repeated keystrokes on the emulated PS2 keyboard
  when using VNC, since the kernel's timers are now much shorter.

  Fix by reporting all-zeroes for CPUID 0x15. This allows guests to fall
  back to using the 8254 to calibrate the local APIC frequency.

  Future work could be to compute values returned for 0x15 that would
  match the host TSC and bhyve local APIC frequency, though all dependencies
  on this would need to be examined (for example, Linux will start using
  0x16 for some hosts).

  PR:   246321
  Reported by:  Jason Tubnor (and tested)
  Reviewed by:  jhb
  Approved by:  jhb, bz (mentor)
  MFC after:    3 days
  Differential Revision:        https://reviews.freebsd.org/D24837

Changes:
  head/sys/amd64/vmm/x86.c
  head/sys/amd64/vmm/x86.h

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