[PATCH v2 3/4] KVM: arm64: Pass pmu events to hyp via vcpu

[Fuad Tabba]

Hi Marc,

On Mon, May 9, 2022 at 11:31 AM Marc Zyngier <maz at kernel.org> wrote:
>
> On Mon, 09 May 2022 10:54:59 +0100,
> Fuad Tabba <tabba at google.com> wrote:
> >
> > Instead of the host accessing hyp data directly, pass the pmu
> > events of the current cpu to hyp via the vcpu.
> >
> > This adds 64 bits (in two fields) to the vcpu that need to be
> > synced before every vcpu run in nvhe and protected modes.
> > However, it isolates the hypervisor from the host, which allows
> > us to use pmu in protected mode in a subsequent patch.
> >
> > No functional change intended.
> >
> > Signed-off-by: Fuad Tabba <tabba at google.com>
> > ---
> >  arch/arm64/include/asm/kvm_host.h |  8 ++------
> >  arch/arm64/kvm/hyp/nvhe/switch.c  | 20 ++++++--------------
> >  arch/arm64/kvm/pmu-emul.c         |  3 +++
> >  arch/arm64/kvm/pmu.c              | 12 ++++--------
> >  include/kvm/arm_pmu.h             |  6 ++++++
> >  5 files changed, 21 insertions(+), 28 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index dfd360404dd8..90476e713643 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -273,14 +273,8 @@ struct kvm_cpu_context {
> >       struct kvm_vcpu *__hyp_running_vcpu;
> >  };
> >
> > -struct kvm_pmu_events {
> > -     u32 events_host;
> > -     u32 events_guest;
> > -};
> > -
> >  struct kvm_host_data {
> >       struct kvm_cpu_context host_ctxt;
> > -     struct kvm_pmu_events pmu_events;
> >  };
> >
> >  struct kvm_host_psci_config {
> > @@ -763,6 +757,7 @@ void kvm_set_sei_esr(struct kvm_vcpu *vcpu, u64 syndrome);
> >  struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
> >
> >  DECLARE_KVM_HYP_PER_CPU(struct kvm_host_data, kvm_host_data);
> > +DECLARE_PER_CPU(struct kvm_pmu_events, kvm_pmu_events);
> >
> >  static inline void kvm_init_host_cpu_context(struct kvm_cpu_context *cpu_ctxt)
> >  {
> > @@ -821,6 +816,7 @@ void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu);
> >  void kvm_set_pmu_events(u32 set, struct perf_event_attr *attr);
> >  void kvm_clr_pmu_events(u32 clr);
> >
> > +struct kvm_pmu_events *kvm_get_pmu_events(void);
> >  void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu);
> >  void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu);
> >  #else
> > diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> > index 0716163313d6..c61120ec8d1a 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> > @@ -153,13 +153,9 @@ static void __hyp_vgic_restore_state(struct kvm_vcpu *vcpu)
> >  /*
> >   * Disable host events, enable guest events
> >   */
> > -static bool __pmu_switch_to_guest(struct kvm_cpu_context *host_ctxt)
> > +static bool __pmu_switch_to_guest(struct kvm_vcpu *vcpu)
> >  {
> > -     struct kvm_host_data *host;
> > -     struct kvm_pmu_events *pmu;
> > -
> > -     host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
> > -     pmu = &host->pmu_events;
> > +     struct kvm_pmu_events *pmu = &vcpu->arch.pmu.events;
> >
> >       if (pmu->events_host)
> >               write_sysreg(pmu->events_host, pmcntenclr_el0);
> > @@ -173,13 +169,9 @@ static bool __pmu_switch_to_guest(struct kvm_cpu_context *host_ctxt)
> >  /*
> >   * Disable guest events, enable host events
> >   */
> > -static void __pmu_switch_to_host(struct kvm_cpu_context *host_ctxt)
> > +static void __pmu_switch_to_host(struct kvm_vcpu *vcpu)
> >  {
> > -     struct kvm_host_data *host;
> > -     struct kvm_pmu_events *pmu;
> > -
> > -     host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
> > -     pmu = &host->pmu_events;
> > +     struct kvm_pmu_events *pmu = &vcpu->arch.pmu.events;
> >
> >       if (pmu->events_guest)
> >               write_sysreg(pmu->events_guest, pmcntenclr_el0);
> > @@ -304,7 +296,7 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> >       host_ctxt->__hyp_running_vcpu = vcpu;
> >       guest_ctxt = &vcpu->arch.ctxt;
> >
> > -     pmu_switch_needed = __pmu_switch_to_guest(host_ctxt);
> > +     pmu_switch_needed = __pmu_switch_to_guest(vcpu);
> >
> >       __sysreg_save_state_nvhe(host_ctxt);
> >       /*
> > @@ -366,7 +358,7 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> >       __debug_restore_host_buffers_nvhe(vcpu);
> >
> >       if (pmu_switch_needed)
> > -             __pmu_switch_to_host(host_ctxt);
> > +             __pmu_switch_to_host(vcpu);
> >
> >       /* Returning to host will clear PSR.I, remask PMR if needed */
> >       if (system_uses_irq_prio_masking())
> > diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> > index 3dc990ac4f44..08d0551a4e43 100644
> > --- a/arch/arm64/kvm/pmu-emul.c
> > +++ b/arch/arm64/kvm/pmu-emul.c
> > @@ -406,6 +406,9 @@ static void kvm_pmu_update_state(struct kvm_vcpu *vcpu)
> >       if (!kvm_vcpu_has_pmu(vcpu))
> >               return;
> >
> > +     if (!has_vhe())
> > +             pmu->events = *kvm_get_pmu_events();
>
> A bit of context:
>
>                 preempt_disable();
>
>                 /*
>                  * The VMID allocator only tracks active VMIDs per
>                  * physical CPU, and therefore the VMID allocated may not be
>                  * preserved on VMID roll-over if the task was preempted,
>                  * making a thread's VMID inactive. So we need to call
>                  * kvm_arm_vmid_update() in non-premptible context.
>                  */
>                 kvm_arm_vmid_update(&vcpu->arch.hw_mmu->vmid);
>
>                 kvm_pmu_flush_hwstate(vcpu);
>
>                 local_irq_disable();
>
> You *still* are in a context where an interrupt can fire and mess
> things up behind your back. Not good. Also, this is now synchronised
> *twice* per run (once on flush, once on sync). Do we really need this?

Yes of course, it needs to happen after interrupts have been disabled.
Will fix that.

> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.
>
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