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] Re: [PATCH] switch to a known good/static GDT beforekexe

To: "Ian Campbell" <Ian.Campbell@xxxxxxxxxxxxx>, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] switch to a known good/static GDT beforekexec
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Thu, 02 Jul 2009 12:45:16 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Thu, 02 Jul 2009 04:45:49 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <C672547C.884C%keir.fraser@xxxxxxxxxxxxx>
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: <C672500B.8846%keir.fraser@xxxxxxxxxxxxx> <C672547C.884C%keir.fraser@xxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 02.07.09 13:11 >>>
>I have one more question then -- when need_full_gdt(n), why do we always
>unconditionally rewrite the l1es mapping the reserved gdt entries? Shouldn't
>that be done on vcpu creation only and perhaps on compat mode switch (i.e.,
>isn't it wasteful to do it in the context switch path)?

While that's correct, we're talking about a single memory write here (plus
the setup code), which I think is no more wasteful than adding the extra
checking that would be needed to see whether we switch between
compat and !compat (including the !need_full_gdt(p) case, where we
don't know what kind of mapping we currently have).

Jan


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