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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.Fraser@xxxxxxxxxxxx>
Date: Fri, 24 Aug 2007 16:20:21 +0100
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>
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Okay, please try tip of staging tree (c/s 15773).

 -- Keir

On 24/8/07 07:19, "Stefan Berger" <stefanb@xxxxxxxxxx> wrote:

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote on 08/10/2007 09:15:57 PM:

> A good debugging approach will be to write a function that walks the
> pagetables for that virtual address and prints the PTE that maps it.
> Scatter calls to this function between acpi_boot_table_init() and
> acpi_boot_init() and hence narrow down exactly where the PTE is
> getting zapped.

What is happening is that the pl1e pointer used for mapping the ACPI table entry changes between the calls before paging_init() and after. The l1_pgentry_t that is used before paging_init() correctly shows that the page is present whereas the one used after indicates that the page is not present. Then when the ACPI table is mapped after paging_init() the tlb is not flushed and wrong information is read.


>  -- Keir
> On 10/8/07 19:21, "Keir Fraser" <keir@xxxxxxxxxxxxx> wrote:

> On 10/8/07 18:00, "Stefan Berger" <stefanb@xxxxxxxxxx> wrote:

> (XEN) map_pages_to_xen : 3533                                     
> (that's the line number)
> (XEN) 0xfff9b000 was NOT present.
> Something between (*) and here seems to trash this presence flag.
> paging_init() and many others lie in between the upper call and this
> one here. Could be a side effect of this? Maybe that tlb flush at
> the right place in one of these functions would solve the problem?
> Yes, this now looks likely and that’s rather scary. We’ll go after
> this next week.

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