| Message ID | 1507809534-10721-1-git-send-email-mpe@ellerman.id.au (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 2a3d6553cbd791da4fb624c2500b4580b3f9d72f |
| Headers | show |
| Series | [1/4] powerpc/tm: Add commandline option to disable hardware transactional memory | expand |
On Thu, 2017-10-12 at 11:58:54 UTC, Michael Ellerman wrote: > Currently we use CPU_FTR_TM to decide if the CPU/kernel can support > TM (Transactional Memory), and if it's true we advertise that to > Qemu (or similar) via KVM_CAP_PPC_HTM. > > PPC_FEATURE2_HTM is the user-visible feature bit, which indicates that > the CPU and kernel can support TM. Currently CPU_FTR_TM and > PPC_FEATURE2_HTM always have the same value, either true or false, so > using the former for KVM_CAP_PPC_HTM is correct. > > However some Power9 CPUs can operate in a mode where TM is enabled but > TM suspended state is disabled. In this mode CPU_FTR_TM is true, but > PPC_FEATURE2_HTM is false. Instead a different PPC_FEATURE2 bit is > set, to indicate that this different mode of TM is available. > > It is not safe to let guests use TM as-is, when the CPU is in this > mode. So to prevent that from happening, use PPC_FEATURE2_HTM to > determine the value of KVM_CAP_PPC_HTM. > > Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Applied to powerpc next. https://git.kernel.org/powerpc/c/2a3d6553cbd791da4fb624c2500b45 cheers
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c index 3480faaf1ef8..a3746b98ec11 100644 --- a/arch/powerpc/kvm/powerpc.c +++ b/arch/powerpc/kvm/powerpc.c @@ -644,8 +644,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) break; #endif case KVM_CAP_PPC_HTM: - r = cpu_has_feature(CPU_FTR_TM_COMP) && - is_kvmppc_hv_enabled(kvm); + r = is_kvmppc_hv_enabled(kvm) && + (cur_cpu_spec->cpu_user_features2 & PPC_FEATURE2_HTM_COMP); break; default: r = 0;
Currently we use CPU_FTR_TM to decide if the CPU/kernel can support TM (Transactional Memory), and if it's true we advertise that to Qemu (or similar) via KVM_CAP_PPC_HTM. PPC_FEATURE2_HTM is the user-visible feature bit, which indicates that the CPU and kernel can support TM. Currently CPU_FTR_TM and PPC_FEATURE2_HTM always have the same value, either true or false, so using the former for KVM_CAP_PPC_HTM is correct. However some Power9 CPUs can operate in a mode where TM is enabled but TM suspended state is disabled. In this mode CPU_FTR_TM is true, but PPC_FEATURE2_HTM is false. Instead a different PPC_FEATURE2 bit is set, to indicate that this different mode of TM is available. It is not safe to let guests use TM as-is, when the CPU is in this mode. So to prevent that from happening, use PPC_FEATURE2_HTM to determine the value of KVM_CAP_PPC_HTM. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> --- arch/powerpc/kvm/powerpc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)