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Re: [Xen-devel] [PATCH] [Xen] Check FADT's signature

To: Keir Fraser <keir@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] [Xen] Check FADT's signature
From: Stefan Berger <stefanb@xxxxxxxxxx>
Date: Fri, 10 Aug 2007 12:11:14 -0400
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>, xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
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xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote on 08/10/2007 11:58:21 AM:

> So the bug could be either that the read is getting hoisted above
> the pagetable update (unlikely) or that there is a stale TLB entry
> (more likely). You could discount the first possibility by replacing
> your local_flush_tlb_pge() with mb() at the end of
> map_pages_to_xen(). If that does not fix the bug then the problem is
> not that the read is getting hoisted.
>
> The TLB handling looks correct though — if the modified PTE was not
> previously empty then we execute an INVLPG on that virtual address.
> Might be worth adding some tracing around there to see if the code
> thinks the PTE was previously present, and hence whether the INVLPG
> actually gets executed?


local_flush_tlb_one() does NOT get executed the first time, but upon the second attempt.
The mb() alone did NOT help.

  Stefan

>
>  -- Keir
>
> On 10/8/07 16:35, "Stefan Berger" <stefanb@xxxxxxxxxx> wrote:

> Keir Fraser <keir@xxxxxxxxxxxxx> wrote on 08/10/2007 11:09:43 AM:
>
> > Not by my reading of the code, but your testing shows differently ;-)
> >
> > Have you tried adding tracing to map_pages_to_xen()? That’s the guts
> > of the remapping code.
>
> Now I did...

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