[Xen-devel] Re: [RFC PATCH 15/33] move segment checks to subarch

[Zachary Amsden <zach@xxxxxxxxxx>]

Arjan van de Ven wrote:
> On Tue, 2006-07-18 at 00:00 -0700, Chris Wright wrote:
>   
> > plain text document attachment (i386-segments)
> > We allow for the fact that the guest kernel may not run in ring 0.
> > This requires some abstraction in a few places when setting %cs or
> > checking privilege level (user vs kernel).
> >     
>   
> > -       regs.xcs = __KERNEL_CS;
> > +       regs.xcs = get_kernel_cs();
> >     
> Hi,
>
> wouldn't this patch be simpler if __KERNEL_CS just became the macro that
> currently is get_kernel_cs() for the XEN case? then code like this
> doesn't need changing at all...
>   
The tradeoff is that then you can't use __KERNEL_CS is assembler code, 
and it is used in entry.S to detect NMI / debug trap workarounds - which 
don't actually need to be paravirtualized, as it is easier to hide the 
nasty cases which cause those side effects.
Zach

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