The following commit has been merged into the x86/splitlock branch of tip: Commit-ID: d28397eaf4c27947a1ffc720d42e8b3a33ae1e2a Gitweb: https://git.kernel.org/tip/d28397eaf4c27947a1ffc720d42e8b3a33ae1e2a Author: Fenghua Yu <fenghua.yu@xxxxxxxxx> AuthorDate: Mon, 19 Apr 2021 21:49:58 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Tue, 18 May 2021 16:39:31 +02:00 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@xxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx> Link: https://lore.kernel.org/r/20210419214958.4035512-5-fenghua.yu@xxxxxxxxx --- Documentation/x86/buslock.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/Documentation/x86/buslock.rst b/Documentation/x86/buslock.rst index 159ff6b..7c051e7 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.
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