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@xxxxxxxxxxxxxxx # v3.14+
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxx>
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