[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] Task Switching and Xen-SVM

  • To: "Petersson, Mats" <Mats.Petersson@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: "Vivek Mohan" <vivek.mt@xxxxxxxxx>
  • Date: Fri, 27 Oct 2006 14:37:41 +0530
  • Delivery-date: Fri, 27 Oct 2006 02:08:29 -0700
  • Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=XQSpHXG7VjoiXkYNsLHnwe2MZOrZJgYlJcqrrhWwT0/bE6OvLT44dBGhqhrjGxoAWu0jrdwTsh3A6GLIML+Gn4W3nzgst7X5G6byNxkoa7t5c4c98Js+3Z+kUQwNrGhVaGrNndaEFm4oqMUCpRlwW/vrpjJsxpv6iMmTfUFIU3c=
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

True, not really many OSes, atleast the ones that matter, use task
switching, but I was just wondering how well Xen w/ HVM would scale as
a full architectural simulator - apparently not.

Any idea why SVM (or VMX) have no support for non-intrusive stepwise
execution of guest VMs?


On 10/27/06, Petersson, Mats <Mats.Petersson@xxxxxxx> wrote:
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> Vivek Mohan
> Sent: 27 October 2006 07:29
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] Task Switching and Xen-SVM
> Hi,
> I was just going through the (svm.c) svm_vmexit_handler() in the SVM
> part of Xen, and saw that:
>          __hvm_bug(regs);
>          break;
> task switches are not intercepted and handled. I was wondering if it
> is not so, then how do you manage consistency of the VM if the Guest
> does a task switch (which could alter the value of CR3)? Am I missing
> something here?

AMD and Intel are doing the same thing here.

Do you actually know of any (32-bit) OS that uses task switching? In my
experience, it's horribly slow (because it generally saves/restores more
of the context than is necessary). Of course, in 64-bit mode it's not
even allowed, all task-management features have been removed... I'm
saying 32-bit OS, since there's probably some 16-bit OS's out there that
do use task-switching, but those OS's are not able to run on current Xen
anyways, since Xen in it's current form is very poor at supporting
segments with base != 0 in protected mode. So far I've only seen a few
rare reports of anyone actually wishing to run a 16-bit OS...

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

Sig9.com  - Sugar for your brain

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.