msr

Documentation

Overview

msr -- read and write MSRs with regular command or Forth

Synopsis:

msr [OPTIONS] r glob MSR
msr [OPTIONS] w glob MSR value
msr [OPTIONS] forth-word [forth-word ...]

Description:

This program reads and writes sets of MSRs, while allowing
them to by changed on a core by core or collective basis.

To read the msrs for 0 (sorry, the command is msr and the forth command
is msr, making this a bit confusing):
sudo msr 0 msr 0x3a reg rd
Breaking that down:
0 - for cpu 0
msr - for take the glob, in this case 0, and push all matching filenames on the stack
0x3a - for register 0x3a
reg - convert to 32-bit integer and push
rd - pop a 32-bit int and a []string and use them to read 1 or more MSRs

for all:
sudo msr "'*" msr 0x3a reg rd

The "'" is needed to quote the * so forth does not think we're multiplying.

Here is a breakdown, running msr with each command in turn:
rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/cmds/core/msr$ ./msr 0
0
rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/cmds/core/msr$ ./msr 0 msr
[/dev/cpu/0/msr]
rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/cmds/core/msr$ ./msr 0 msr 0x3a
[[/dev/cpu/0/msr] 0x3a]
rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/cmds/core/msr$ ./msr 0 msr 0x3a reg
[[/dev/cpu/0/msr] 58]
rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/cmds/core/msr$ ./msr 0 msr 0x3a reg rd
[0]
rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/cmds/core/msr$

To read, then write all of them
(the dup is so we have the msr list at TOS -- it's just a convenience)
sudo msr 0 msr dup 0x3a reg rd 0x3a reg swap 1 u64 or wr
to just write them

Also, note, all the types are checked by assertions. The reg has to be
32 bits, the val 64

more examples:
read reg 0x3a and leave the least of MSRs and values on TOS, to be
printed at exit.

sudo msr "'"* msr dup 0x3a reg rd
[[/dev/cpu/0/msr /dev/cpu/1/msr /dev/cpu/2/msr /dev/cpu/3/msr] [5 5 5 5]]

From there, the write is easy:
sudo msr "'"* msr dup 0x3a reg rd 0x3a reg swap wr

For convenience, we maintain the old read and write commands:
msr r <glob> <register>
msr w <glob> <register> <value>

Yep, it's a bit inconvenient; the idea is that in the simple case,
you will use the r and w commands. For programmatic cases, you can
work to build up a working set of arguments.

For example, I started with
msr "'"* msr
and, once I saw the MSR selection was OK, built the command up from
there. At each step I could see the stack and whether I was going the
right direction.

The old commands remain: rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/cmds/core/msr$ sudo ./msr r 0 0x3a [5] rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/cmds/core/msr$ sudo ./msr w 0 0x3a 5 [5]

For a view of what Forth is doing, run with -d.

msr reads and writes msrs using a Forth interpreter on argv

Synopsis:

To see what is available:
msr words

Description:

msr provides a set of Forth words that let you manage MSRs.
You can add new ones of your own.
For a start, it provides some pre-defined words for well-known MSRs

push a [] of MSR names and the 0x3a register on the stack
IA32_FEATURE_CONTROL -- equivalent to * msr 0x3a reg
The next two commands use IA32_FEATURE_CONTROL:
READ_IA32_FEATURE_CONTROL -- equivalent to IA32_FEATURE_CONTROL rd
LOCK IA32_FEATURE_CONTROL -- equivalent to IA32_FEATURE_CONTROL rd IA32_FEATURE_CONTROL 1 u64 or wr
e.g.

./msr IA32_FEATURE_CONTROL [[/dev/cpu/0/msr /dev/cpu/1/msr /dev/cpu/2/msr /dev/cpu/3/msr] 58]

As a special convenience, we have two useful cases:
r glob register -- read the MSR 'register' from cores matching 'glob'
w glob register value -- write the value to 'register' on all cores matching 'glob'

Examples:

Show the IA32 feature MSR on all cores
sudo fio READ_IA32_FEATURE_CONTROL
[[5 5 5 5]]
lock the registers
sudo fio LOCK_IA32_FEATURE_CONTROL
Just see it one core 0 and 1
sudo ./fio '[01]' msr 0x3a reg rd
[[5 5]]