• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Treat POWER9 CPU threads as independent subcores · 45c940ba
    Paul Mackerras authored
    With POWER9, each CPU thread has its own MMU context and can be
    in the host or a guest independently of the other threads; there is
    still however a restriction that all threads must use the same type
    of address translation, either radix tree or hashed page table (HPT).
    
    Since we only support HPT guests on a HPT host at this point, we
    can treat the threads as being independent, and avoid all of the
    work of coordinating the CPU threads.  To make this simpler, we
    introduce a new threads_per_vcore() function that returns 1 on
    POWER9 and threads_per_subcore on POWER7/8, and use that instead
    of threads_per_subcore or threads_per_core in various places.
    
    This also changes the value of the KVM_CAP_PPC_SMT capability on
    POWER9 systems from 4 to 1, so that userspace will not try to
    create VMs with multiple vcpus per vcore.  (If userspace did create
    a VM that thought it was in an SMT mode, the VM might try to use
    the msgsndp instruction, which will not work as expected.  In
    future it may be possible to trap and emulate msgsndp in order to
    allow VMs to think they are in an SMT mode, if only for the purpose
    of allowing migration from POWER8 systems.)
    
    With all this, we can now run guests on POWER9 as long as the host
    is running with HPT translation.  Since userspace currently has no
    way to request radix tree translation for the guest, the guest has
    no choice but to use HPT translation.
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    45c940ba
powerpc.c 33.8 KB