Re: [PATCH v3 3/4] KVM: arm64: Pass pmu events to hyp via vcpu

[Oliver Upton <oupton@google.com>]

On Mon, May 09, 2022 at 12:03:29PM +0000, Fuad Tabba 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 visible side effects in behavior intended.
> 
> Signed-off-by: Fuad Tabba <tabba@google.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  8 ++------
>  arch/arm64/kvm/arm.c              | 15 +++++++++++++++
>  arch/arm64/kvm/hyp/nvhe/switch.c  | 20 ++++++--------------
>  arch/arm64/kvm/pmu.c              | 12 ++++--------
>  include/kvm/arm_pmu.h             |  6 ++++++
>  5 files changed, 33 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;
> -};
> -

Looks like you're moving this to arm_pmu.h as well. Probably a better
home for it, but unclear why it is done in this patch.

>  struct kvm_host_data {
>  	struct kvm_cpu_context host_ctxt;
> -	struct kvm_pmu_events pmu_events;
>  };
>  

Are we going to need this struct any more since it now has a single
member?

>  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);

Why do you need this declaration? I don't see the percpu data being
accessed outside of pmu.c.

>  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/arm.c b/arch/arm64/kvm/arm.c
> index 2adb5832a756..86bcdb2a23a8 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -817,6 +817,19 @@ static int noinstr kvm_arm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
>  	return ret;
>  }
>  
> +/*
> + * Updates the vcpu's view of the pmu events for this cpu.
> + * Must be called before every vcpu run after disabling interrupts, to ensure
> + * that an interrupt cannot fire and update the structure.
> + */
> +static void kvm_pmu_update_vcpu_events(struct kvm_vcpu *vcpu)
> +{
> +	if (has_vhe() || !kvm_vcpu_has_pmu(vcpu))
> +		return;
> +
> +	vcpu->arch.pmu.events = *kvm_get_pmu_events();
> +}
> +
>  /**
>   * kvm_arch_vcpu_ioctl_run - the main VCPU run function to execute guest code
>   * @vcpu:	The VCPU pointer
> @@ -882,6 +895,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  
>  		kvm_vgic_flush_hwstate(vcpu);
>  
> +		kvm_pmu_update_vcpu_events(vcpu);
> +
>  		/*
>  		 * Ensure we set mode to IN_GUEST_MODE after we disable
>  		 * interrupts and before the final VCPU requests check.
> 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.c b/arch/arm64/kvm/pmu.c
> index 4bd38ff34221..c19bf6e4969e 100644
> --- a/arch/arm64/kvm/pmu.c
> +++ b/arch/arm64/kvm/pmu.c
> @@ -5,7 +5,8 @@
>   */
>  #include <linux/kvm_host.h>
>  #include <linux/perf_event.h>
> -#include <asm/kvm_hyp.h>
> +
> +DEFINE_PER_CPU(struct kvm_pmu_events, kvm_pmu_events);
>  
>  /*
>   * Given the perf event attributes and system type, determine
> @@ -25,14 +26,9 @@ static bool kvm_pmu_switch_needed(struct perf_event_attr *attr)
>  	return (attr->exclude_host != attr->exclude_guest);
>  }
>  
> -static struct kvm_pmu_events *kvm_get_pmu_events(void)
> +struct kvm_pmu_events *kvm_get_pmu_events(void)

Why not make this function visible in patch 1? It seems benign even
though there are no other users at that moment outside of the
compilation unit.

--
Thanks,
Oliver

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