[PATCH 0/6] KVM: PPC: Book3S HV: Run HPT guests on radix hosts

[PATCH 0/6] KVM: PPC: Book3S HV: Run HPT guests on radix hosts

[Paul Mackerras]

Currently, on POWER9 machines using HV KVM, the host kernel will use
one or other of the two MMU modes available, HPT (hashed page table)
or radix, and all KVM guests must use the same MMU mode.  This is
inconvenient because it means that a guest on a radix host can't run a
legacy OS that doesn't know about POWER9.  On the other hand, if the
host is booted in HPT mode so that legacy guest kernels can be run,
then neither the host nor any other guest can take advantage of the
radix MMU mode.

To further complicate matters, current POWER9 chips have the
restriction that all SMT threads in each core must use the same MMU
mode (HPT or radix), though they can be in different partitions.

This patch series adds the ability to run HPT guests on a host in
radix mode.  In order to comply with the restriction of not mixing HPT
and radix threads on the same core, we take a similar approach to that
already used on POWER8, namely, run the host in single-threaded mode
(only thread 0 of each core online), and have KVM be able to wake up
the other threads when a KVM guest is to be run, and use the other
threads for running guest VCPUs.

So that KVM knows whether it should be managing individual threads on
POWER9 (as it does currently) or whole cores, we add a new module
parameter called "indep_threads_mode".  This is normally Y on POWER9
but must be set to N before any HPT guests can be run on a radix
host.  The value of indep_threads_mode is sampled at the time of
creation of each guest, and the value at the time of creation is what
applies to that guest for the whole of its lifetime.  It is preferable
to change indep_threads_mode only when no guests are running.

In order to allow HPT guests to run on a radix host, the following
commands (or their equivalents) are required first:

# echo N >/sys/module/kvm_hv/parameters/indep_threads_mode
# ppc64_cpu --smt=off

KVM will run up to four vcpus on each core using the existing dynamic
micro-threading code.  This can be controlled using the
target_smt_mode module parameter.

This patch series is against my kvm-ppc-next branch.

Paul.

 arch/powerpc/include/asm/kvm_book3s_64.h  | 116 ++++++++++--
 arch/powerpc/include/asm/kvm_book3s_asm.h |  17 +-
 arch/powerpc/include/asm/kvm_host.h       |   3 +-
 arch/powerpc/include/asm/kvm_ppc.h        |   2 +
 arch/powerpc/kernel/asm-offsets.c         |   3 +
 arch/powerpc/kernel/idle_book3s.S         |  35 ++--
 arch/powerpc/kvm/book3s_64_mmu_hv.c       |  67 ++++---
 arch/powerpc/kvm/book3s_64_mmu_radix.c    |   1 +
 arch/powerpc/kvm/book3s_hv.c              | 305 +++++++++++++++++++-----------
 arch/powerpc/kvm/book3s_hv_builtin.c      |  99 +++++++++-
 arch/powerpc/kvm/book3s_hv_rm_mmu.c       |  11 +-
 arch/powerpc/kvm/book3s_hv_rmhandlers.S   |  73 +++++--
 arch/powerpc/kvm/powerpc.c                |   3 +-
 13 files changed, 523 insertions(+), 212 deletions(-)