Re: [PATCH] kdump: Save parameter segment in protected mode (x86)

[ebiederm@xmission.com (Eric W. Biederman)]

Ack.  This is a simple fix to a very practical problem, for
using the kernel from a reserved area of memory.

Vivek Goyal <vgoyal@in.ibm.com> writes:

> o With introduction of kexec as boot-loader, the assumption that parameter
>   segment will always be loaded at lower address than kernel and will be 
>   addressable by early bootup page tables is no longer valid. In kexec on 
>   panic case parameter segment might well be loaded beyond kernel image and 
>   might not be addressable by early boot page tables.
> o This case might hit in the scenario where user has reserved a chunk of
>   memory for second kernel, for example 16MB to 64MB, and has also built 
>   second kernel for physical memory location 16MB. In this case kexec has no 
>   choice but to load the parameter segment at a higher address than new kernel 
>   image at safe location where new kernel does not stomp it. 
> o Though problem should automatically go away once relocatable kernel for i386 
>   is in place and kexec can determine the location of new kernel at run time
>   and load parameter segment at lower address than kernel image. But till then
>   this patch can go in (assuming it does not break something else). 
> o This patch moves up the boot parameter saving code. Now boot parameters
>   are copied out in protected mode before page tables are initialized. This
>   will ensure that parameter segment is always addressable irrespective of
>   its physical location.
>
>
> Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>