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Re: [Xen-devel] [patch] pae: tlbflush linear page table updates

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [patch] pae: tlbflush linear page table updates
From: Gerd Knorr <kraxel@xxxxxxx>
Date: Tue, 9 Aug 2005 09:54:14 +0200
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On Mon, Aug 08, 2005 at 05:52:29PM +0100, Keir Fraser wrote:
> On 8 Aug 2005, at 15:51, Gerd Knorr wrote:
> >On l3 page dir updates (and related linear page table updates)
> >we'll have to flush the tlb to make sure the linear page access
> >goes to the correct pages ...
> Have you actually observed problems without the flush?

Yes.  PAE xenlinux (UP) didn't boot up.  The first
make_page_readonly() faults because the first copy_from_user()
in ptwr_do_page_fault() fails (which dereferences stuff using
the linear page table ...).

I hoped the tlbflush also fixes the SMP issues, but it doesn't,
so there are more bugs.  I'm not sure the PAE/SMP crashes are
ptwr related, they also happen (although a bit less likely it
seems) without writable page tables.


panic("it works"); /* avoid being flooded with debug messages */

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