linux-kernel - Re: [Xen-devel] [PATCHv1] x86: don't schedule when handling #NM exception

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Date:	Tue, 18 Mar 2014 11:17:53 -0700
From:	Sarah Newman <srn@...mr.com>
To:	George Dunlap <george.dunlap@...citrix.com>,
	Jan Beulich <JBeulich@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	Ingo Molnar <mingo@...hat.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Xen-devel] [PATCHv1] x86: don't schedule when handling #NM exception

On 03/17/2014 10:14 AM, George Dunlap wrote:
> On 03/17/2014 05:05 PM, Jan Beulich wrote:
>>>>> On 17.03.14 at 17:55, "H. Peter Anvin" <hpa@...or.com> wrote:
>>> So if this interface wasn't an accident it was active negligence and
>>> incompetence.
>> I don't think so - while it (as we now see) disallows certain things
>> inside the guest, back at the time when this was designed there was
>> no sign of any sort of allocation/scheduling being done inside the
>> #NM handler. And furthermore, a PV specification is by its nature
>> allowed to define deviations from real hardware behavior, or else it
>> wouldn't be needed in the first place.
> 
> But it's certainly the case that deviating from the hardware in *this* way by default was always
> very likely to case the exact kind of bug we've seen here.  It is an "interface trap" that was bound
> to be tripped over (much like Intel's infamous sysret vulnerability).
> 
> Making it opt-in would have been a much better idea.  But the people who made that decision are long
> gone, and we now need to deal with the situation as we have it.

Should or has there been a review of the current xen PVABI to look for any other such deviations?
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