From mboxrd@z Thu Jan  1 00:00:00 1970
From: George Dunlap <george.dunlap@eu.citrix.com>
Subject: Re: [PATCH] x86: Control CR0 TS behavior using
	dev_na_ts_allowed
Date: Mon, 17 Mar 2014 14:05:43 +0000
Message-ID: <53270137.7000600@eu.citrix.com>
References: <53266841.6090308@prgmr.com>
	<1395027059-26248-1-git-send-email-srn@prgmr.com>
	<5326C2820200007800124905@nat28.tlf.novell.com>
	<CAFLBxZawWhtdkaV9u0ye=_R32y7pD=QdWoSu13OYGxiBQXTk5Q@mail.gmail.com>
	<5327081D0200007800124BCD@nat28.tlf.novell.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"; Format="flowed"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Received: from mail6.bemta3.messagelabs.com ([195.245.230.39])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <George.Dunlap@citrix.com>) id 1WPYAm-00027n-Qp
	for xen-devel@lists.xenproject.org; Mon, 17 Mar 2014 14:05:49 +0000
In-Reply-To: <5327081D0200007800124BCD@nat28.tlf.novell.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Jan Beulich <JBeulich@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>, xen-devel <xen-devel@lists.xenproject.org>, Yanhai Zhu <zhu.yanhai@gmail.com>, David Vrabel <david.vrabel@citrix.com>, Sarah Newman <srn@prgmr.com>
List-Id: xen-devel@lists.xenproject.org

On 03/17/2014 01:35 PM, Jan Beulich wrote:
>>>> On 17.03.14 at 13:42, George Dunlap <George.Dunlap@eu.citrix.com> wrote:
>> On Mon, Mar 17, 2014 at 8:38 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>>> On 17.03.14 at 04:30, Sarah Newman <srn@prgmr.com> wrote:
>>> Not being convinced at all that this is the right approach (in
>>> particular it remains unclear how an affected guest should deal with
>>> running on a hypervisor not supporting the new interface)
>> It looks like the intention of this patch was that if the dom0
>> administrator enables the new option, then it will be on by default,
>> *but* the guest can disable the new behavior.  That way, if an admin
>> knows that she's running all PVOPS kernels (no "classic Xen" kernels),
>> she can enable it system-wide.  Older PVOPS kernels will behave
>> correctly (but a bit slowly), and newer PVOPS kernels will switch to
>> the PVABI behavior and reap the performance benefit.
>>
>> Newer PVOPS kernels running on older hypervisors will simply use the
>> PVABI behavior.
> But if that works correctly, then there's no hypervisor/tools
> change needed in the first place.

Yes, there's still a need to run *old* PVOPS kernels on *new* 
hypervisors.  That (as I understand it) is the point of this patch.

  -George