Downplaying a serious issue

[Allan Jude]

On 2014-04-03 09:08, 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).

Not very much detail has been provided about what exactly 'is not
working' in these other hypervisors. I would hesitate to write that
FreeBSD 10 doesn't work in Xen from a single user report, when Colin
Percival has FreeBSD 10 images for 32bit Amazon EC2 (Xen) that I've
heard no reports of problems with

http://www.daemonology.net/freebsd-on-ec2/

> 
> 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?

The 'unmapped IO' feature was added in FreeBSD 10, so the feature that
is related to (if not causing) the problem is new.

> 
> 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?
> 
> Regards, Frank.
> 
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-- 
Allan Jude

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