Re: [Xen-devel] real-mode switch

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 5/6/07 14:24, "Petersson, Mats" <Mats.Petersson@xxxxxxx> wrote:

>> I am trying to switch to real-mode to make some BIOS calls.
>> However, when I try to remap kernel at virtual address 0 I
>> get "Unable to handle kernel paging request at virtual
>> address c06e0000" error. Here is where I get it:
>> 
>> memcpy(swapper_pg_dir, swapper_pg_dir + USER_PGD_PTRS,
>> sizeof(swapper_pg_dir[0]) * KERNEL_PGD_PTRS);
> 
> You can't remap the kernel to 0 - you'll have to use the Hypervisor if
> you want to get to real-mode, I think. There was some talk about making
> a hypercall to "call this bit of code as real-mode".

Actually I changed my mind on this. Returning to real mode after system boot
is just too dangerous.

But anyway, the immediate problem in this case is the memcpy(). You have to
update page directory entries with the mmu_update hypercall.

 -- Keir


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