  We demonstrate that supernova remnant (SNR) shocks embedded within massive
star clusters can reproduce both the cosmic-ray proton and all-particle spectra
measured in the vicinity of the Earth up to hundreds of peta-electronvolts
(PeV). We model two classes of massive star clusters. The first population are
"loose clusters" which do not power a collective wind termination shock. SNR
shocks then expand in a low-density and weakly magnetised medium, and this
population mainly contributes up to the "knee" of the CR spectrum around 1 PeV.
The second population are young compact clusters, which are powerful and
compact enough to sustain a collective wind outflow. SNR shocks then expand
from the cluster into the strongly magnetised wind and accelerate nuclei up to
ultra-high energies. This population, representing only about 15% of all
Galactic massive star clusters, nevertheless dominates the spectrum between ~ 1
and 100 PeV. While these two components alone can reproduce the shape of the CR
spectrum up to hundreds of PeV, adding a light sub-ankle extragalactic
component motivated by composition and anisotropy measurements, allows to
reproduce the spectrum up to the highest energies. Fitting parameters are
systematically linked to physical variables whose values are in line with
theoretical expectations.
