From owner-freebsd-virtualization@freebsd.org  Wed Apr 12 08:58:40 2017
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To: freebsd-virtualization@FreeBSD.org, Peter Grehan <grehan@FreeBSD.org>
From: Andriy Gapon <avg@FreeBSD.org>
Subject: dos in bhyve
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Date: Wed, 12 Apr 2017 11:56:11 +0300
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I wonder if anyone was able to run any DOS variant in bhyve.

I tried FreeDOS using BHYVE_UEFI_CSM firmware, but it seems to just hang.

I also tried adding a frame buffer device, it seems that there is some reaction
to key presses (RET) sent via VNC, but the screen stays black, so it's
impossible to tell if there are any prompts and what happens.
In any case, after a few RET-s the guest crashes with a triple fault.
Seems like that happens when it enables paging.

Some data from the VM state after the crash.
Last instructions:
mov    %eax,%cr0
mov    $0x110000,%edi      <=========== triple fault here

cr0[0]          0x0000000080000033
cr3[0]          0x0000000000115000
cr4[0]          0x00000000000006a0

I wonder if it's the value of CR4 that causes the trouble (PAE bit set).

-- 
Andriy Gapon