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From: "tip-bot2 for Fenghua Yu" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tony Luck <tony.luck@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: x86/splitlock] Documentation/x86: Add ratelimit in buslock.rst
Date: Tue, 18 May 2021 14:44:21 -0000	[thread overview]
Message-ID: <162134906105.29796.18308488746834241121.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210419214958.4035512-5-fenghua.yu@intel.com>

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@intel.com>
AuthorDate:    Mon, 19 Apr 2021 21:49:58 
Committer:     Thomas Gleixner <tglx@linutronix.de>
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@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

---
 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.

  reply	other threads:[~2021-05-18 14:44 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-19 21:49 [PATCH 0/4] x86/bus_lock: Set rate limit for bus lock Fenghua Yu
2021-04-19 21:49 ` [PATCH 1/4] Documentation/x86: Add buslock.rst Fenghua Yu
2021-05-18 14:39   ` Thomas Gleixner
2021-05-18 14:44   ` [tip: x86/splitlock] " tip-bot2 for Fenghua Yu
2021-08-18  1:59     ` Xiaoyao Li
2021-08-18 15:36       ` Fenghua Yu
2021-08-19  3:36         ` Xiaoyao Li
2021-04-19 21:49 ` [PATCH 2/4] x86/bus_lock: Set rate limit for bus lock Fenghua Yu
2021-05-18 14:44   ` [tip: x86/splitlock] " tip-bot2 for Fenghua Yu
2021-04-19 21:49 ` [PATCH 3/4] Documentation/admin-guide: Change doc for bus lock ratelimit Fenghua Yu
2021-05-18 14:44   ` [tip: x86/splitlock] Documentation/admin-guide: Add " tip-bot2 for Fenghua Yu
2021-04-19 21:49 ` [PATCH 4/4] Documentation/x86: Add ratelimit in buslock.rst Fenghua Yu
2021-05-18 14:44   ` tip-bot2 for Fenghua Yu [this message]
2021-05-17 18:46 ` [PATCH 0/4] x86/bus_lock: Set rate limit for bus lock Fenghua Yu
2021-05-17 19:01   ` Thomas Gleixner
2021-05-17 19:05     ` Fenghua Yu

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