Subject: Re: [PATCH v2 14/18] KVM: arm64: spe: Provide guest virtual interrupts for SPE

From: Marc Zyngier <[email-masked]>
Date: Sun, 22 Dec 2019 12:07:50 +0000

On Fri, 20 Dec 2019 14:30:21 +0000,
Andrew Murray <[email-masked]> wrote:
> 
> Upon the exit of a guest, let's determine if the SPE device has generated
> an interrupt - if so we'll inject a virtual interrupt to the guest.
> 
> Upon the entry and exit of a guest we'll also update the state of the
> physical IRQ such that it is active when a guest interrupt is pending
> and the guest is running.
> 
> Finally we map the physical IRQ to the virtual IRQ such that the guest
> can deactivate the interrupt when it handles the interrupt.
> 
> Signed-off-by: Andrew Murray <[email-masked]>
> ---
>  include/kvm/arm_spe.h |  6 ++++
>  virt/kvm/arm/arm.c    |  5 ++-
>  virt/kvm/arm/spe.c    | 71 +++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 81 insertions(+), 1 deletion(-)
> 
> diff --git a/include/kvm/arm_spe.h b/include/kvm/arm_spe.h
> index 9c65130d726d..91b2214f543a 100644
> --- a/include/kvm/arm_spe.h
> +++ b/include/kvm/arm_spe.h
> @@ -37,6 +37,9 @@ static inline bool kvm_arm_support_spe_v1(void)
>  						      ID_AA64DFR0_PMSVER_SHIFT);
>  }
>  
> +void kvm_spe_flush_hwstate(struct kvm_vcpu *vcpu);
> +inline void kvm_spe_sync_hwstate(struct kvm_vcpu *vcpu);
> +
>  int kvm_arm_spe_v1_set_attr(struct kvm_vcpu *vcpu,
>  			    struct kvm_device_attr *attr);
>  int kvm_arm_spe_v1_get_attr(struct kvm_vcpu *vcpu,
> @@ -49,6 +52,9 @@ int kvm_arm_spe_v1_enable(struct kvm_vcpu *vcpu);
>  #define kvm_arm_support_spe_v1()	(false)
>  #define kvm_arm_spe_irq_initialized(v)	(false)
>  
> +static inline void kvm_spe_flush_hwstate(struct kvm_vcpu *vcpu) {}
> +static inline void kvm_spe_sync_hwstate(struct kvm_vcpu *vcpu) {}
> +
>  static inline int kvm_arm_spe_v1_set_attr(struct kvm_vcpu *vcpu,
>  					  struct kvm_device_attr *attr)
>  {
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 340d2388ee2c..a66085c8e785 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -741,6 +741,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  		preempt_disable();
>  
>  		kvm_pmu_flush_hwstate(vcpu);
> +		kvm_spe_flush_hwstate(vcpu);
>  
>  		local_irq_disable();
>  
> @@ -782,6 +783,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  		    kvm_request_pending(vcpu)) {
>  			vcpu->mode = OUTSIDE_GUEST_MODE;
>  			isb(); /* Ensure work in x_flush_hwstate is committed */
> +			kvm_spe_sync_hwstate(vcpu);
>  			kvm_pmu_sync_hwstate(vcpu);
>  			if (static_branch_unlikely(&userspace_irqchip_in_use))
>  				kvm_timer_sync_hwstate(vcpu);
> @@ -816,11 +818,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  		kvm_arm_clear_debug(vcpu);
>  
>  		/*
> -		 * We must sync the PMU state before the vgic state so
> +		 * We must sync the PMU and SPE state before the vgic state so
>  		 * that the vgic can properly sample the updated state of the
>  		 * interrupt line.
>  		 */
>  		kvm_pmu_sync_hwstate(vcpu);
> +		kvm_spe_sync_hwstate(vcpu);

The *HUGE* difference is that the PMU is purely a virtual interrupt,
while you're trying to deal with a HW interrupt here.

>  
>  		/*
>  		 * Sync the vgic state before syncing the timer state because
> diff --git a/virt/kvm/arm/spe.c b/virt/kvm/arm/spe.c
> index 83ac2cce2cc3..097ed39014e4 100644
> --- a/virt/kvm/arm/spe.c
> +++ b/virt/kvm/arm/spe.c
> @@ -35,6 +35,68 @@ int kvm_arm_spe_v1_enable(struct kvm_vcpu *vcpu)
>  	return 0;
>  }
>  
> +static inline void set_spe_irq_phys_active(struct arm_spe_kvm_info *info,
> +					   bool active)
> +{
> +	int r;
> +	r = irq_set_irqchip_state(info->physical_irq, IRQCHIP_STATE_ACTIVE,
> +				  active);
> +	WARN_ON(r);
> +}
> +
> +void kvm_spe_flush_hwstate(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_spe *spe = &vcpu->arch.spe;
> +	bool phys_active = false;
> +	struct arm_spe_kvm_info *info = arm_spe_get_kvm_info();
> +
> +	if (!kvm_arm_spe_v1_ready(vcpu))
> +		return;
> +
> +	if (irqchip_in_kernel(vcpu->kvm))
> +		phys_active = kvm_vgic_map_is_active(vcpu, spe->irq_num);
> +
> +	phys_active |= spe->irq_level;
> +
> +	set_spe_irq_phys_active(info, phys_active);

So you're happy to mess with the HW interrupt state even when you
don't have a HW irqchip? If you are going to copy paste the timer code
here, you'd need to support it all the way (no, don't).

> +}
> +
> +void kvm_spe_sync_hwstate(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_spe *spe = &vcpu->arch.spe;
> +	u64 pmbsr;
> +	int r;
> +	bool service;
> +	struct kvm_cpu_context *ctxt = &vcpu->arch.ctxt;
> +	struct arm_spe_kvm_info *info = arm_spe_get_kvm_info();
> +
> +	if (!kvm_arm_spe_v1_ready(vcpu))
> +		return;
> +
> +	set_spe_irq_phys_active(info, false);
> +
> +	pmbsr = ctxt->sys_regs[PMBSR_EL1];
> +	service = !!(pmbsr & BIT(SYS_PMBSR_EL1_S_SHIFT));
> +	if (spe->irq_level == service)
> +		return;
> +
> +	spe->irq_level = service;
> +
> +	if (likely(irqchip_in_kernel(vcpu->kvm))) {
> +		r = kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id,
> +					spe->irq_num, service, spe);
> +		WARN_ON(r);
> +	}
> +}
> +
> +static inline bool kvm_arch_arm_spe_v1_get_input_level(int vintid)
> +{
> +	struct kvm_vcpu *vcpu = kvm_arm_get_running_vcpu();
> +	struct kvm_spe *spe = &vcpu->arch.spe;
> +
> +	return spe->irq_level;
> +}

This isn't what such a callback is for. It is supposed to sample the
HW, an nothing else.

> +
>  static int kvm_arm_spe_v1_init(struct kvm_vcpu *vcpu)
>  {
>  	if (!kvm_arm_support_spe_v1())
> @@ -48,6 +110,7 @@ static int kvm_arm_spe_v1_init(struct kvm_vcpu *vcpu)
>  
>  	if (irqchip_in_kernel(vcpu->kvm)) {
>  		int ret;
> +		struct arm_spe_kvm_info *info;
>  
>  		/*
>  		 * If using the SPE with an in-kernel virtual GIC
> @@ -57,10 +120,18 @@ static int kvm_arm_spe_v1_init(struct kvm_vcpu *vcpu)
>  		if (!vgic_initialized(vcpu->kvm))
>  			return -ENODEV;
>  
> +		info = arm_spe_get_kvm_info();
> +		if (!info->physical_irq)
> +			return -ENODEV;
> +
>  		ret = kvm_vgic_set_owner(vcpu, vcpu->arch.spe.irq_num,
>  					 &vcpu->arch.spe);
>  		if (ret)
>  			return ret;
> +
> +		ret = kvm_vgic_map_phys_irq(vcpu, info->physical_irq,
> +					    vcpu->arch.spe.irq_num,
> +					    kvm_arch_arm_spe_v1_get_input_level);

You're mapping the interrupt int the guest, and yet you have never
forwarded the interrupt the first place. All this flow is only going
to wreck the host driver as soon as an interrupt occurs.

I think you should rethink the interrupt handling altogether. It would
make more sense if the interrupt was actually completely
virtualized. If you can isolate the guest state and compute the
interrupt state in SW (and from the above, it seems that you can),
then you shouldn't mess with the whole forwarding *at all*, as it
isn't designed for devices shared between host and guests.

	M.

-- 
Jazz is not dead, it just smells funny.

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