RE: [Xen-devel] WP flag in CR0, setting

["Bruce Rogers" <BROGERS@xxxxxxxxxx>]

I haven't examined what Linux is doing to validate correct handling of
the WP bit, but
NetWare operates without setting CR0.WPt, and that is one of the issues
with NetWare
not working in fully virtualized mode.

The shadow paging code does not  process the page tables according to
CR0.WP == 0
semantics.

- Bruce

>>> On 6/16/2006 at 6:50 PM, in message
<8FFF7E42E93CC646B632AB40643802A82E9441@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"Nakajima, Jun" <jun.nakajima@xxxxxxxxx> wrote:
> It should be working in HVM guest. See, for example:
> 
> ...
> Memory: 3040444k/3071992k available (1918k kernel code, 30156k
reserved,
> 775k data, 176k init, 2154492k highmem)
> Checking if this processor honours the WP bit even in supervisor
mode...
> Ok.
> Calibrating delay using timer specific routine.. 4803.94 BogoMIPS
> (lpj=9607882)
> ...
> 
> Jun
> ---
> Intel Open Source Technology Center 
> 
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir
Fraser
> Sent: Thursday, June 15, 2006 1:09 AM
> To: Simon Kagstrom
> Cc: xen-devel list
> Subject: Re: [Xen-devel] WP flag in CR0, setting
> 
> 
> On 15 Jun 2006, at 09:00, Simon Kagstrom wrote:
> 
>>> We can't support this. We rely on write protection for all sorts
of
>>> things (e.g., prevent guest write access to page tables). You'll
have
>>> to temporarily make the mapping writable, or make a kernel-private
>>> writable mapping.
>>
>> Thanks for the explanation. Would the WP flag work in a HVM
setting?
> 
> It may not be supported right now, but it would be easy to do so if
not.
> 
>   -- Keir
> 
> 
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