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

[Marc Zyngier <maz@kernel.org>]

On Mon, 09 May 2022 10:54:59 +0100,
Fuad Tabba <tabba@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@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?

Thanks,

	M.

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