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/
Home Products Support Community News


Re: [Xen-devel] [RFC] event channels and xen callbacks

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC] event channels and xen callbacks
From: Mathieu Ropert <mro@xxxxxxxxxx>
Date: Wed, 12 Apr 2006 17:56:18 +0200
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Thu, 13 Apr 2006 04:58:32 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <c8101a489dc2c5f538cfde5c723a8b62@xxxxxxxxxxxx>
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/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <44329A63.2020808@xxxxxxxxxx> <c8101a489dc2c5f538cfde5c723a8b62@xxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mozilla Thunderbird 1.0.7 (X11/20051013)
Keir Fraser wrote:

On 4 Apr 2006, at 17:10, Mathieu Ropert wrote:

i'm currently playing a bit with event channels and hypervisor callbacks, and i find myself stuck because i miss some informations. Maybe you can give me some hints:

on amd64 arch, i'd like to know about hypervisor callback: ie, stack layout when called by Xen, stack location in memory (is it using the TSS entry as hardware traps do?) and finally, about how HYPERVISOR_iret() expects to find the stack upon call (like when you used iret? or something else?).

I may write a little paper or tutorial from i've learned and didn't found in Xen doc after i get a better view of the whole thing...

1. The stack layout on callback is just as for a native hardware interrupt or exception. Those exceptions that push an error code when running natively also do so when running on Xen, for example.

2. The TSS isn't fully virtualised by Xen -- instead you register your kernel stack with the stack_switch() hypercall. Calling this is equivalent to writing your stack pointer into your TSS when running natively.

3. When calling HYPERVISOR_iret() there should be a iret_context swtructure at the top of the stack. See its definition, and a big comment, in xen/include/public/arch-x86_64.h.

 -- Keir


all those helped me alot, but i'm now getting some trouble with my callback handler. I can't figure out why, but Xen call it with some odd rsp (about 5 pages below the rsp i have when the callback occur). I'm still in kernel mode when the callback happen (from what i saw, when processing events before returning to guest after an hypercall) so my stack isn't supposed to be changed from what i heard. Oddly, this isn't happening with my trap handlers (i tried to trigger some faults and dump the stack, all is fine) which are supposed to have the same behavior. The only difference i see is that bounce frame is created in Xen by the syscall handler and not by the trap handler, but shouldn't be any different, should it? Have anyone ever got this issue, maybe i forgot to setup something prior to enabling events...


Xen-devel mailing list

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