rumpkernel and bhyve: triple faults

[Rodney W. Grimes]

> > Hello lists,
> > 
> > I?m currently playing around with getting rump kernels built with rumpkernel(7) running on FreeBSD?s bhyve(4). I?m using a custom boot loader [1] which builds on some patches to bhyveload / user boot [2].
> > 
> > To test, I?m using a simple ?helloer? unikernel from the tutorial [3]:
> > 
> ... excelent discription of your debug process removed for breif reply ...
> 
> > Due to compiler optimisations, the check here isn?t the
> > (hypervisor == HYPERVISOR_XEN) check directly after the call to hypervisor_detect,
> > but the check (bios_crtc_base == 0) in
> 
> bios_crtc_base would be part of the isa legacy vga
> controller card.  Bhyve does not, at this time, or
> in the near future expect to have, support for this
> legacy device.

I am wrong on this, the framebuffer device does
infact have support for the legacy i/o addresses
that this should point to.  You should see the
"vgaconf" section of the FrameBuffer section
of the bhyve(8) manpage.

I believe you need to be running bhyve with the
uefi bios options, the with CMS version, and
have vgaconf=on to get your code to work as is.

> > rumprun/platform/hw/arch/x86/cons.c:59:
> >    649   0     350887182668 vm testing[0]: handled exception vmexit at 0x102a56
> > 
> > Therefore, I?m assuming this is the origin of the fault.
> > 
> > Tracking down bios_crtc_base, I find that it?s loaded in
> > rumprun/platform/hw/arch/amd64/locore.S:70:
> > 
> > 	/* save BIOS data area values */
> > 	movw BIOS_COM1_BASE, %bx
> > 	movw %bx, bios_com1_base
> > 	movw BIOS_CRTC_BASE, %bx
> > 	movw %bx, bios_crtc_base
> > 
> > Where BIOS_CRTC_BASE is 0x463 and BIOS_COM1_BASE is 0x400. Checking the bhyve
> > device node in /dev/vmm with xxd(1), I find the words at these addresses to be
> > Uninitialised:
> > 
> > 00000400: 0000                                     ..
> > 00000483: 0000                                     ..
> Typo here, should this be 00000463?
> 
> 
> > I?m not sure where to go from here. Is this a bug in bhyve(4),
> No, it is not a bug, it is an unimplemented device.
> 
> > should these
> > values be initialised somehow, or should I patch rumpkernel(7) to skip this check
> > when running on bhyve(4)?
> rumpkernel is assuming or requiring the presence of legacy isa hardware,
> it should probably be taught that this may not exist.  You could simply
> skip this check, but I expect you would then have a harder to find
> failure later when it tries to use the hardware it expects to be
> there.
> 
> > 
> > Fabian
>  
> ... Full KTR trace removed for breif reply ...

-- 
Rod Grimes                                                 rgrimes at freebsd.org