WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] [semi-urgent Xen CS question] Re: git commit 9fd67b4ed07

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] [semi-urgent Xen CS question] Re: git commit 9fd67b4ed0714ab718f1f9bd14c344af336a6df7 (x86-64: Give vvars their own page) breaks Xen PV guests (64-bit).
From: Andrew Lutomirski <luto@xxxxxxx>
Date: Fri, 29 Jul 2011 08:51:19 -0400
Cc: Keir Fraser <keir.xen@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Delivery-date: Fri, 29 Jul 2011 05:52:23 -0700
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; bh=5yPR4o+nvnyBMhaab24dXTSQJnCWmxHTAqFaI89QV3Y=; b=EuPkBhBKAEhB6jSk4sXgoAFXwLYW7rCrUKI3TG7dyQ+umwwXNfPFrbBLx8YkbVM3IQ RzexXMOra2aB1MkQS8CMeRpDPazjPEg81mkWEn20ihh/cgASwMe7rd5Zky6IFBIledmE hZFWHKm0U/L8RB2tdlMJ/K4lYTT1RvO2DllYk=
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4E30FCAE.4070906@xxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <CAObL_7HYJLN3Eq2Q4ESuU4=4230Xs37C6Jqn1OYApr2LXTvo3Q@xxxxxxxxxxxxxx> <CA54E6A4.1E91B%keir.xen@xxxxxxxxx> <CAObL_7G31QbwkRdmzf8ABFTmsKbmca=KPkQNM2J_jgT6VG6JqQ@xxxxxxxxxxxxxx> <CAObL_7Emqw0wg1pkvgYQBF7uPm5xCjFUpWsTso61-WRSoCtFzQ@xxxxxxxxxxxxxx> <1093cd3a-acfe-49ab-b410-9fb49b139816@xxxxxxxxxxxxxxxxx> <CAObL_7E1g_PqongTRm-Hve7ERurPtUh+JAj+1JGOTeOLK9mz4A@xxxxxxxxxxxxxx> <4E30317E.30706@xxxxxxxx> <CAObL_7FWi-kK0rK2m8OwTUEQtPZQZ0iP88A8WSkb4CNdu2YqLQ@xxxxxxxxxxxxxx> <4E3048B4.6020805@xxxxxxxx> <CAObL_7H9LVaXrXu_-2zOgri2XEVzJaE2VywciG1EJF56NJL0jA@xxxxxxxxxxxxxx> <4E30FCAE.4070906@xxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
On Thu, Jul 28, 2011 at 2:07 AM, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> On 07/27/2011 09:33 PM, Andrew Lutomirski wrote:
>> On Sandy Bridge, a null vsyscall takes 373 ns. Without
>> VCGF_in_syscall, it's 457 ns. The change causes my little test app to
>> get cs == __USER_CS.
>
> Hm, 20% is more noticable than I would hope.  What about a regular syscall?

VCGF_in_syscall: gettimeofday() (the syscall version) takes 593 ns.
Without VCGF_in_syscall, it's 712 ns.

I'd argue for using my original approach of adding a user_64bit_mode
function -- I think it's a legitimate cleanup and Xen, for better or
worse, really does have two long mode CPL 3 selectors.  If we removed
selector 6 from the GDT, that would be a different story, but that
would probably be a more intrusive change.

--Andy

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

<Prev in Thread] Current Thread [Next in Thread>