Build.md

@@ -138,7 +138,12 @@ This is only possible on local file systems. A feasible way is to use the [[likw
 
 If you are using cgroups and access is not allowed although you tried all the steps above, check whether access to the `msr` device files is denied by cgroup's `devices.deny` or not explicitly allowed in `devices.allow`.
 
+**Update for Linux kernel 5.9 and newer:**
+With Linux 5.9, the `msr` kernel module got some security fixes. The major change for LIKWID is, that now all MSR are non-writable by default. In order to change that, you have to change the boot options of your operating system to contain `msr.allow_writes=on` to enable writes again. This affects only `ACCESSMODE=direct` and `ACCESSMODE=accessdaemon`. If you use the `perf_event` backend, you don't have to change anything.
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+
 # Installation on Intel Xeon Phi (KNC)
+
 In order to build LIKWID for the Xeon Phi, set the `COMPILER` option in config.mk to `MIC` and build it on a host that has a MIC-aware Intel compiler and the MPSS installed. Moreover, there might be the problem that the required Intel libraries are not present on the Xeon Phi and you need to copy them. Commonly the libraries are `libimf.so`, `libsvml.so`, `libirng.so` and `libintlc.so.5`. LIKWID assumes that they are copied in the same path as the LIKWID library `liblikwid.so` (`$INSTALLED_PREFIX/lib`). If you install them somewhere different, please set the `RPATHS` variable in config.mk or make/include_MIC.mk to point to the location.
 
 Moreover, the Intel Xeon Phi has some limit of running processes and since every CPU needs its access daemon, LIKWID would start many processes. Therefore, LIKWID allows only direct access to the MSR device files on Xeon Phi. In order to allow this, set the suid-root bit for the Lua interpreter (`sudo chmod u+s $INSTALLED_PREFIX/bin/likwid-lua`).