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xen-devel
Re: [Xen-devel] Task Switching and Xen-SVM
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?
-Vivek
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:
>
> case VMEXIT_TASK_SWITCH:
> __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...
--
Mats
>
> Thanks,
> Vivek
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
>
>
>
--
http://sig9.com/vivek/
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