| Message ID | 20170606070908.GB20869@fergus.ozlabs.ibm.com |
|---|---|
| State | Superseded |
| Headers | show |
On 06.06.2017 09:09, Paul Mackerras wrote: > This adds code to save the values of three SPRs (special-purpose > registers) used by userspace to control event-based branches (EBBs), > which are essentially interrupts that get delivered directly to > userspace. These registers are loaded up with guest values when > entering the guest, and their values are saved when exiting the > guest, but we were not saving the host values and restoring them > before going back to userspace. > > On POWER8 this would only affect userspace programs which explicitly > request the use of EBBs and also use the KVM_RUN ioctl, since the > only source of EBBs on POWER8 is the PMU, and there is an explicit > enable bit in the PMU registers (and those PMU registers do get > properly context-switched between host and guest). On POWER9 there > is provision for externally-generated EBBs, and these are not subject > to the control in the PMU registers. > > Since these registers only affect userspace, we can save them when > we first come in from userspace and restore them before returning to > userspace, rather than saving/restoring the host values on every > guest entry/exit. Similarly, we don't need to worry about their > values on offline secondary threads since they execute in the context > of the idle task, which never executes in userspace. > > Fixes: b005255e12a3 ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08) > Cc: stable@vger.kernel.org # v3.14+ > Signed-off-by: Paul Mackerras <paulus@ozlabs.org> > --- > arch/powerpc/kvm/book3s_hv.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c > index 1344da7..66740cb 100644 > --- a/arch/powerpc/kvm/book3s_hv.c > +++ b/arch/powerpc/kvm/book3s_hv.c > @@ -3102,6 +3102,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu) > { > int r; > int srcu_idx; > + unsigned long ebb_regs[3] = {}; /* shut up GCC */ > > if (!vcpu->arch.sane) { > run->exit_reason = KVM_EXIT_INTERNAL_ERROR; > @@ -3129,6 +3130,13 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu) > > flush_all_to_thread(current); > > + /* Save userspace EBB register values */ > + if (cpu_has_feature(CPU_FTR_ARCH_207S)) { > + ebb_regs[0] = mfspr(SPRN_EBBHR); > + ebb_regs[1] = mfspr(SPRN_EBBRR); > + ebb_regs[2] = mfspr(SPRN_BESCR); > + } > + > vcpu->arch.wqp = &vcpu->arch.vcore->wq; > vcpu->arch.pgdir = current->mm->pgd; > vcpu->arch.state = KVMPPC_VCPU_BUSY_IN_HOST; > @@ -3155,6 +3163,13 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu) > } > } while (is_kvmppc_resume_guest(r)); > > + /* Restore userspace EBB register values */ > + if (cpu_has_feature(CPU_FTR_ARCH_207S)) { > + mtspr(SPRN_EBBHR, ebb_regs[0]); > + mtspr(SPRN_EBBRR, ebb_regs[1]); > + mtspr(SPRN_BESCR, ebb_regs[2]); > + } > + > out: > vcpu->arch.state = KVMPPC_VCPU_NOTREADY; > atomic_dec(&vcpu->kvm->arch.vcpus_running); Reviewed-by: Thomas Huth <thuth@redhat.com> -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 1344da7..66740cb 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -3102,6 +3102,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu) { int r; int srcu_idx; + unsigned long ebb_regs[3] = {}; /* shut up GCC */ if (!vcpu->arch.sane) { run->exit_reason = KVM_EXIT_INTERNAL_ERROR; @@ -3129,6 +3130,13 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu) flush_all_to_thread(current); + /* Save userspace EBB register values */ + if (cpu_has_feature(CPU_FTR_ARCH_207S)) { + ebb_regs[0] = mfspr(SPRN_EBBHR); + ebb_regs[1] = mfspr(SPRN_EBBRR); + ebb_regs[2] = mfspr(SPRN_BESCR); + } + vcpu->arch.wqp = &vcpu->arch.vcore->wq; vcpu->arch.pgdir = current->mm->pgd; vcpu->arch.state = KVMPPC_VCPU_BUSY_IN_HOST; @@ -3155,6 +3163,13 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu) } } while (is_kvmppc_resume_guest(r)); + /* Restore userspace EBB register values */ + if (cpu_has_feature(CPU_FTR_ARCH_207S)) { + mtspr(SPRN_EBBHR, ebb_regs[0]); + mtspr(SPRN_EBBRR, ebb_regs[1]); + mtspr(SPRN_BESCR, ebb_regs[2]); + } + out: vcpu->arch.state = KVMPPC_VCPU_NOTREADY; atomic_dec(&vcpu->kvm->arch.vcpus_running);
This adds code to save the values of three SPRs (special-purpose registers) used by userspace to control event-based branches (EBBs), which are essentially interrupts that get delivered directly to userspace. These registers are loaded up with guest values when entering the guest, and their values are saved when exiting the guest, but we were not saving the host values and restoring them before going back to userspace. On POWER8 this would only affect userspace programs which explicitly request the use of EBBs and also use the KVM_RUN ioctl, since the only source of EBBs on POWER8 is the PMU, and there is an explicit enable bit in the PMU registers (and those PMU registers do get properly context-switched between host and guest). On POWER9 there is provision for externally-generated EBBs, and these are not subject to the control in the PMU registers. Since these registers only affect userspace, we can save them when we first come in from userspace and restore them before returning to userspace, rather than saving/restoring the host values on every guest entry/exit. Similarly, we don't need to worry about their values on offline secondary threads since they execute in the context of the idle task, which never executes in userspace. Fixes: b005255e12a3 ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08) Cc: stable@vger.kernel.org # v3.14+ Signed-off-by: Paul Mackerras <paulus@ozlabs.org> --- arch/powerpc/kvm/book3s_hv.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)