Re: Removing the PVH assert in arch/x86/hvm/io.c:87

[David Vrabel <david.vrabel@citrix.com>]

On 05/12/14 11:07, Roger Pau Monné wrote:
> El 05/12/14 a les 10.15, Jan Beulich ha escrit:
>>>>> On 04.12.14 at 17:35, <roger.pau@citrix.com> wrote:
>>> I've just stumbled upon this assert while testing PVH on different
>>> hardware. It was added in 7c4870 as a safe belt, but it turns out INS
>>> and OUTS go through handle_mmio. So using this instructions from a PVH
>>> guest basically kills Xen.
>>>
>>> I've removed it and everything seems fine, so I'm considering sending a
>>> patch for 4.5 in order to have it removed. I think the path that could
>>> trigger the crash because of the missing vioapic stuff is already
>>> guarded by the other chunk added in the same patch.
>>
>> Iirc we settled on forbidding paths to handle_mmio() for PVH (hence
>> the ASSERT()). Sadly you provide way too little detail on what is
>> actually happening in your case: What's the use case of to-be-
>> emulated INS/OUTS in a PVH kernel?
> 
> In this specific situation I'm seeing intsw instructions executed by the
> FreeBSD ATA layer:
> 
> http://fxr.watson.org/fxr/source/dev/ata/ata-lowlevel.c#L740

Why are you running this device driver at all in a PVH guest?  It should
only be using PV block devices.

David