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

To: Stefan Berger <stefanb@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] [Xen] Check FADT's signature
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Fri, 10 Aug 2007 16:58:21 +0100
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>
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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?

 -- 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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