[Bug 203682] Slow boot under VMware Fusion w/ UEFI firmware and SMP -- until APs are launched

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203682

            Bug ID: 203682
           Summary: Slow boot under VMware Fusion w/ UEFI firmware and SMP
                    -- until APs are launched
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: marcel at FreeBSD.org

Host:
- Mac OS 10.10
- Mac OS 10.11
Hypervisor:
- VMware Fusion 7 Pro
- VMware Fusion 8 Pro
VM configuration:
- UEFI firmware
- UEFI console (std 1024x768)
- Multiple CPUs (minimal 2)
- RAM (don't care AFAICT)

Description:
As soon as FreeBSD takes the APs out of INIT and has them spinning in a tight
loop and until until the APs are launched, the UEFI frame buffer is *very*
slow. It takes 1 or 2 seconds to scroll 1 line of characters (in graphics
mode).

After the APs are launched, frame buffer access reverts to normal.

>From the code (init_secondary_tail() in sys/x86/x86/mp_x86.c) it looks like the
APs, while waiting to be unleashed, are not completely configured yet. In
particular (and this comes from a gut feeling) the PAT MR is configured until
the end (see pmap_init_pat() in sys/amd64/amd64/pmap.c). I wonder if the APs,
while not being configured completely, cause the H/W (VMware Fusion in this
case) to behave erratically.

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