Reserving physical memory space as early as possible in Linux boot-time - linux

Question

I am trying to find a way to reserve physical memory for a proprietary memory type hardware as early as possible after system boots up (Linux CentOs with Intel Xeon server platform).
I did the following at setup_arch() in arch/x86/kernel/setup.c and it works, but found out that I am not allowed to patch the kernel. The requirement is no BIOS and kernel mod.
setup_arch()
{
....
// Calls a proprietary function that returns custom proprietary memory module's starting address and size.
memblock_reserve(mem_start_addr, mem_size);
.....
}
I cannot use memmap=xx/xx either at Grub, because the start and size of the device is unknown (it has to be "discovered" by software)
Is there any way to do this?

Answer 1

One idea is to write a custom grub module and set memmap=xx using it.
The following is how to do it.
Note that following method only works above CentOS 7 since CentOS 6.x or below uses grub 0.9x .
In that case, you may have to modify code of grub 0.9x and replace /boot/grub/stage1 or /boot/grub/stage2
$ git clone git://git.savannah.gnu.org/grub.git
$ cd grub
$ git checkout grub-2.02-beta2 # CentOS 7 currently uses grub-2.02-beta
$ vim grub-core/Makefile.core.def # add following row
module = {
name = my_custom_module;
common = lib/my_custom_module.c;
};
$ vim grub-core/lib/my_custom_module.c # create following file
#include <grub/dl.h>
#include <grub/env.h>
GRUB_MOD_LICENSE ("GPLv3+");
GRUB_MOD_INIT(my_custom_module){
// Calls a proprietary function that returns custom proprietary memory module's starting address and size.
const char *mem_size = "123";
grub_env_set("my_memsize",mem_size);
}
GRUB_MOD_FINI(my_custom_module){
}
$ ./autogen.sh
$ ./configure
$ make
Now you can find that grub-core/my_custom_module.mod is created.
so copy it to /boot/grub2/i386-pc/ (or whatever your *.mod file exists)
Edit the grub.conf and add something like
insmod my_custom_module
linux /boot/vmlinuz-3.10.el7.x86_64 root=UUID=1a3b5c7d9 ro memmap=${my_memsize}