Re: Kexec query about what makes sure control pages/page tables are not overwritten

[H. Peter Anvin]

It is pretty simple: the kernel exports how much text+data+bss+brk it needs, and the kernel cannot use memory outside that region until it is ready to control the address space itself.

Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
>Hi,
>
>I am staring at control page allocation logic in case of kdump and
>wondering what makes sure that these pages are not overwritten by 
>next kernel.
>
>I see that for 64bit entry, control pages have the page tables needed
>for second kernel. In case of crash these pages from from crash kernel
>reserved region. Page allocator is very simple and that is start from
>lowest crash reserved range and move higher and allocate first
>available
>page which is not allocated to segments. What makes sure that these
>pages
>are not overwritten by second kernel.
>
>I guess it becomes a general bootloader question. How do we make sure
>bootloader prepared page tables/gdt will not be overwritten by kernel
>(till kernel sets up its own page tables and gdt) and how should we do
>the
>allocation and placement.
>
>Thanks
>Vivek

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