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Re: Never mind Re: [Xen-devel] Re: Xen reboots when trying to start new

To: Kip Macy <kmacy@xxxxxxxxxxxxxxx>
Subject: Re: Never mind Re: [Xen-devel] Re: Xen reboots when trying to start new domain
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 10 Sep 2004 03:53:04 +0100
Cc: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx
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You could look at the Linux 2.6 sparse tree and look for where
CONFIG_WRITABLE_PAGETABLE is used. That'd tell you how it differs from
the old-style interface.

Basically, when building the domain you use DOM0_VMASSIST to specify
that the domain wishes to use writable page tables. Then, when you
want to modify a pte, just write directly to it. And... that's it!

Note that we don't support direct writing to pde's (yet), only to leaf
entries in the multi-level page table.

 -- Keir

> I'm hitting a bug in the pmap code when switching to multi-user mode. It
> looks to me like a bug in Xen, but I don't know for sure yet. I'd like
> to try turning on writable pagetables and use the stock i386 pmap.c code
> to see how much mileage I get out of that. Is there any documentation on
> the writable pagetable interfaces other than wading through the
> changesets?
> 
> 
> Thanks.
> 
>                               -Kip
> 
> 
> 
> On Fri, 10 Sep 2004, Keir Fraser wrote:
> 
> > > I just burned an extra page so I'm not aliasing the page table - so now
> > > it comes up.
> > >
> > >
> > >                                   -Kip
> > >
> >
> > Excellent! I'd encourage you to continue to avoid the aliasing, as it
> > may lead to performance degradation in the future. Once you're up can
> > you kill the low mappings and free the extra page?
> >
> >  -- Keir
> >
> >
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