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| author | Paul Mackerras <paulus@ozlabs.org> | 2016-09-15 13:42:52 +1000 |
|---|---|---|
| committer | Paul Mackerras <paulus@ozlabs.org> | 2016-09-27 14:41:39 +1000 |
| commit | 88b02cf97bb7e742db3e31671d54177e3e19fd89 (patch) | |
| tree | c46f63021dec7147e31aaff330b259b7df13b0da /arch/powerpc/kvm/book3s_hv.c | |
| parent | adad0d02a7d3c958121a4eb9d126015a2353db94 (diff) | |
| download | lwn-88b02cf97bb7e742db3e31671d54177e3e19fd89.tar.gz lwn-88b02cf97bb7e742db3e31671d54177e3e19fd89.zip | |
KVM: PPC: Book3S: Treat VTB as a per-subcore register, not per-thread
POWER8 has one virtual timebase (VTB) register per subcore, not one
per CPU thread. The HV KVM code currently treats VTB as a per-thread
register, which can lead to spurious soft lockup messages from guests
which use the VTB as the time source for the soft lockup detector.
(CPUs before POWER8 did not have the VTB register.)
For HV KVM, this fixes the problem by making only the primary thread
in each virtual core save and restore the VTB value. With this,
the VTB state becomes part of the kvmppc_vcore structure. This
also means that "piggybacking" of multiple virtual cores onto one
subcore is not possible on POWER8, because then the virtual cores
would share a single VTB register.
PR KVM emulates a VTB register, which is per-vcpu because PR KVM
has no notion of CPU threads or SMT. For PR KVM we move the VTB
state into the kvmppc_vcpu_book3s struct.
Cc: stable@vger.kernel.org # v3.14+
Reported-by: Thomas Huth <thuth@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Diffstat (limited to 'arch/powerpc/kvm/book3s_hv.c')
| -rw-r--r-- | arch/powerpc/kvm/book3s_hv.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 9b3bba643b43..c4f8971c954d 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -1199,6 +1199,9 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id, case KVM_REG_PPC_DPDES: *val = get_reg_val(id, vcpu->arch.vcore->dpdes); break; + case KVM_REG_PPC_VTB: + *val = get_reg_val(id, vcpu->arch.vcore->vtb); + break; case KVM_REG_PPC_DAWR: *val = get_reg_val(id, vcpu->arch.dawr); break; @@ -1391,6 +1394,9 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id, case KVM_REG_PPC_DPDES: vcpu->arch.vcore->dpdes = set_reg_val(id, *val); break; + case KVM_REG_PPC_VTB: + vcpu->arch.vcore->vtb = set_reg_val(id, *val); + break; case KVM_REG_PPC_DAWR: vcpu->arch.dawr = set_reg_val(id, *val); break; @@ -2213,9 +2219,11 @@ static bool can_piggyback_subcore(struct kvmppc_vcore *pvc, pvc->lpcr != vc->lpcr) return false; - /* P8 guest with > 1 thread per core would see wrong TIR value */ - if (cpu_has_feature(CPU_FTR_ARCH_207S) && - (vc->num_threads > 1 || pvc->num_threads > 1)) + /* + * P8 guests can't do piggybacking, because then the + * VTB would be shared between the vcpus. + */ + if (cpu_has_feature(CPU_FTR_ARCH_207S)) return false; n_thr = cip->subcore_threads[sub] + pvc->num_threads; |