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Documentation/x86: Add ratelimit in buslock.rst 

ratelimit is a new command line option for bus lock handling. Add proper
documentation.

[ tglx: Massaged documentation ]

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20210419214958.4035512-5-fenghua.yu@intel.com
This commit is contained in:
Fenghua Yu 2021-04-19 21:49:58 +00:00 committed by Thomas Gleixner
parent 9d839c280b
commit d28397eaf4
1 changed files with 22 additions and 0 deletions
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Documentation/x86/buslock.rst
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@ -63,6 +63,11 @@ parameter "split_lock_detect". Here is a summary of different options:
| |When both features are | |
| |supported, fatal in #AC | |
+------------------+----------------------------+-----------------------+
|ratelimit:N |Do nothing |Limit bus lock rate to |
|(0 < N <= 1000) | |N bus locks per second |
| | |system wide and warn on|
| | |bus locks. |
+------------------+----------------------------+-----------------------+
Usages
======
@ -102,3 +107,20 @@ fatal
-----
In this case, the bus lock is not tolerated and the process is killed.
ratelimit
---------
A system wide bus lock rate limit N is specified where 0 < N <= 1000. This
allows a bus lock rate up to N bus locks per second. When the bus lock rate
is exceeded then any task which is caught via the buslock #DB exception is
throttled by enforced sleeps until the rate goes under the limit again.
This is an effective mitigation in cases where a minimal impact can be
tolerated, but an eventual Denial of Service attack has to be prevented. It
allows to identify the offending processes and analyze whether they are
malicious or just badly written.
Selecting a rate limit of 1000 allows the bus to be locked for up to about
seven million cycles each second (assuming 7000 cycles for each bus
lock). On a 2 GHz processor that would be about 0.35% system slowdown.