kasan: docs: update boot parameters section

Update the "Boot parameters" section in KASAN documentation:

 - Mention panic_on_warn.

 - Mention kasan_multi_shot and its interaction with panic_on_warn.

 - Clarify kasan.fault=panic interaction with panic_on_warn.

 - A readability clean-up.

Link: https://lkml.kernel.org/r/01364952f15789948f0627d6733b5cdf5209f83a.1615559068.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/dev-tools/kasan.rst

@@ -174,10 +174,16 @@ call_rcu() and workqueue queuing.
 Boot parameters
 ~~~~~~~~~~~~~~~
 
+KASAN is affected by the generic ``panic_on_warn`` command line parameter.
+When it is enabled, KASAN panics the kernel after printing a bug report.
+
+By default, KASAN prints a bug report only for the first invalid memory access.
+With ``kasan_multi_shot``, KASAN prints a report on every invalid access. This
+effectively disables ``panic_on_warn`` for KASAN reports.
+
 Hardware tag-based KASAN mode (see the section about various modes below) is
 intended for use in production as a security mitigation. Therefore, it supports
-boot parameters that allow to disable KASAN competely or otherwise control
-particular KASAN features.
+boot parameters that allow disabling KASAN or controlling its features.
 
 - ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``).
 
@@ -194,8 +200,8 @@ particular KASAN features.
   traces collection (default: ``on``).
 
 - ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN
-  report or also panic the kernel (default: ``report``). Note, that tag
-  checking gets disabled after the first reported bug.
+  report or also panic the kernel (default: ``report``). The panic happens even
+  if ``kasan_multi_shot`` is enabled.
 
 Implementation details
 ----------------------