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Diffstat (limited to 'Documentation/x86/buslock.rst')
| -rw-r--r-- | Documentation/x86/buslock.rst | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/x86/buslock.rst b/Documentation/x86/buslock.rst index 159ff6ba830e..7c051e714943 100644 --- a/Documentation/x86/buslock.rst +++ b/Documentation/x86/buslock.rst @@ -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. |