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

[Stefan Berger <stefanb@xxxxxxxxxx>]

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.

   Stefan

> 
>  -- 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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