Commit 2a3d6553 authored Oct 12, 2017 by Michael Ellerman

KVM: PPC: Tie KVM_CAP_PPC_HTM to the user-visible TM feature



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>

parent 31a4d448

arch/powerpc/kvm/powerpc.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;