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xen-devel
RE: [Xen-devel] real-mode switch
Can you please explain why you think it is dangerous? Especially if it
is supported by functionality to switch to protected mode right after
"real mode code" is done executing?
Thanks
Jayant
-----Original Message-----
From: Keir Fraser [mailto:keir@xxxxxxxxxxxxx]
Sent: Tuesday, June 05, 2007 7:16 PM
To: Petersson, Mats; Jayant Mangalampalli; ron minnich;
xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] real-mode switch
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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