doc/admin-guide: Note credentials consolidation under CAP_PERFMON

Add note that starting from Linux v5.9 CAP_PERFMON Linux capability is
enough to conduct performance monitoring and observability using
perf_events API.
Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-man@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Link: http://lore.kernel.org/lkml/2b1a92a1-84ce-5c70-837d-8ffe96849588@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Documentation/admin-guide/perf-security.rst

@@ -84,11 +84,14 @@ capabilities then providing the process with CAP_PERFMON capability singly
 is recommended as the preferred secure approach to resolve double access
 denial logging related to usage of performance monitoring and observability.
 
-Unprivileged processes using perf_events system call are also subject
-for PTRACE_MODE_READ_REALCREDS ptrace access mode check [7]_ , whose
-outcome determines whether monitoring is permitted. So unprivileged
-processes provided with CAP_SYS_PTRACE capability are effectively
-permitted to pass the check.
+Prior Linux v5.9 unprivileged processes using perf_events system call
+are also subject for PTRACE_MODE_READ_REALCREDS ptrace access mode check
+[7]_ , whose outcome determines whether monitoring is permitted.
+So unprivileged processes provided with CAP_SYS_PTRACE capability are
+effectively permitted to pass the check. Starting from Linux v5.9
+CAP_SYS_PTRACE capability is not required and CAP_PERFMON is enough to
+be provided for processes to make performance monitoring and observability
+operations.
 
 Other capabilities being granted to unprivileged processes can
 effectively enable capturing of additional data required for later