Downplaying a serious issue

[Glen Barber]

On Thu, Apr 03, 2014 at 02:08:15PM +0100, Frank Leonhardt wrote:
> On 03/04/2014 12:36, Glen Barber wrote:
> >On Thu, Apr 03, 2014 at 09:47:02AM +0200, Torbjorn Granlund wrote:
> >>Glen Barber <gjb at FreeBSD.org> writes:
> >>
> >>   It is not a doc problem.
> >>   The issue is specific to certain hardware configurations, and unless
> >>   anyone has made any breakthroughs that I am unaware of, the cause is
> >>   still unknown.
> >>It happens on:
> >>
> >>AMD piledriver running Linux+KVM
> >>AMD piledriver running Linux+Xen
> >>Intel Nehalem running NetBSD+Xen
> >>Intel Sandybridge running NetBSD+Xen
> >>Intel Haswell running NetBSD+Xen
> >>AMD K10 Barcelona running NetBSD+Xen
> >>AMD Bulldozer running NetBSD+Xen
> >>
> >We need more specifics.
> >
> >>I've seen the laughable claim that this is a "bug in Virtualbox", and now
> >>the major downplay at http://www.freebsd.org/releases/10.0R/errata.html,
> >>where this is a minor hardware specific problem.
> >>
> >>I have not found one piece of PC hardware where it does not happen under
> >>virtualisation.  Please let me know some configuration where FreeBSD/i386
> >>works under a type 1 virtualiser?  Perhaps Bhyve is FreeBSD-compatible?
> >>
> >Does not happen on my VirtualBox host.
> >
> >Glen
> >
> I've been following this discussion with some alarm, but have now looked at
> the Errata:
> 
> ------------------------------------------
> 
> "FreeBSD/i386 10.0-RELEASE running as a guest operating system
> onVirtualBoxcan have a problem with disk I/O access. It depends on some
> specific hardware configuration and does not depend on a specific version
> ofVirtualBoxor host operating system.
> 
> It causes various errors and makes FreeBSD quite unstable. Although the
> cause is still unclear, disabling unmapped I/O works as a workaround."
> etcetera
> 
> -------------------------------------
> 
> I don't read this as "down-playing" - it's up front about saying that
> there's a problem with every version of VirtualBox. It would, of course, be
> useful to add that it doesn't work with other named emulators too (for a
> virtual machine IS emulating the I/O hardware).
> 
> My concern was that this bug may be present on the real hardware too. I
> suspect more people would be running an i386 version as a VM than on real
> metal these days.
> 
> Does the problem exist on previous releases?
> 

No.

> It seems to me that, after research, the list of confirmed incompatible
> configurations need to be expanded, especially to encompass other
> known-to-fail emulations. A list of "confirmed" problem environments would
> make readers wary about untested emulators too.
> 
> Incidentally, I don't see this as a bug in FreeBSD. A hypervisor is supposed
> to transparent to the OS, emulating the hardware that the OS thinks it has,
> to perfection. This is a broken VM, as clearly it's not behaving as the real
> hardware would. Or is it?
> 

The cause is unclear.

Glen

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