| These modules have been merged in upstream GRUB git, so there's no need to build them from this repository. |
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grub2 msr modules to read (rdmsr) or write (wrmsr) from/to model-specific registers.
It allows you to make changes to the MSR before any OS boots:
In this example a Core 2 Extreme CPU is tweaked to allow a higher multiplier than stock.
Main structure inspired by memrw.c and cpuid.c (since it's an i386 module only), assembly code adapted from:
grub-core/commands/i386/rdmsr.c - Registration of the rdmsr command.
include/grub/i386/rdmsr.h - Assembly functions to read from the MSR.
grub-core/commands/i386/rdmsr.c - Registration of the wrmsr command.
include/grub/i386/wrmsr.h - Assembly functions to write to the MSR.
* Use the script build.sh to download the latest version of grub, include the module source
and build everything.
* Use the script install.sh to install the module to the system.
It will perform the following operations:
1. Copy the file rdmsr.mod and wrmsr.mod from /usr/src/grub/grub-core/ to /boot/grub/i386-pc/
2. Add the following lines to the end of /boot/grub/i386-pc/command.lst:
*rdmsr: rdmsr
wrmsr: wrmsr
3. Do the previous operations under the /usr/lib/grub/i386-pc folder if it exists.
4. Edit the file /etc/grub.d/40_custom loading the module and anything else that you need:
#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
insmod wrmsr
wrmsr 0x19A 0x12
rmmod wrmsr
4. Update the grub configuration using:
update-grub
* Use the script uninstall.sh in order to remove the modules from the system.
Once the rdmsr/wrmsr modules are loaded, two new commands are availiable
for reading and writing to the MSR:
rdmsr 0xADDRESS
wrmsr 0xADDRESS 0xVALUE