In recent years the interpretation of high energy cosmic ray measurements took
another direction. From the astrophysical point of view, it was usually
admitted that extra-galactic charged cosmic rays were protons, but mass
composition results for the Pierre Auger Observatory, in particular using
hadronic interaction models updated with LHC data, show that a mixed
composition is observed at energies well above the ankle of the spectrum.
Using these new models in the knee region for KASCADE-Grande data analysis
lead to significant change in the mass composition as well. Realistic air
shower simulation and hadronic interaction models are the key points for a
proper interpretation of charged cosmic ray data. After a first part
dedicated to the CORSIKA and CONEX air shower simulation models and EPOS LHC
and QGSJETII-04 hadronic interaction models, the latest results from the
KASCADE-Grande and Pierre Auger Observatory will be presented with a focus
given on mass composition and constrains on hadronic interactions.