From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: Removing the PVH assert in arch/x86/hvm/io.c:87
Date: Fri, 5 Dec 2014 11:24:26 +0000
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To: =?windows-1252?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.com>, Jan Beulich <JBeulich@suse.com>
Cc: xen-devel@lists.xenproject.org, Tim Deegan <tim@xen.org>
List-Id: xen-devel@lists.xenproject.org

On 05/12/14 11:07, Roger Pau Monn=E9 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