Re: [RFC PATCH 4/4] KVM: x86: Add support for local interrupt requests from userspace

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2015-05-13 03:47, Steve Rutherford wrote:
> In order to enable userspace PIC support, the userspace PIC needs to
> be able to inject local interrupt requests.
> 
> This adds the ioctl KVM_REQUEST_LOCAL_INTERRUPT and kvm exit
> KVM_EXIT_GET_EXTINT.
> 
> The vm ioctl KVM_REQUEST_LOCAL_INTERRUPT makes a KVM_REQ_EVENT request
> on the BSP, which causes the BSP to exit to userspace to fetch the
> vector of the underlying external interrupt, which the BSP then
> injects into the guest. This matches the PIC spec, and is necessary to
> boot Windows.

The API name seems too generic, given the fairly specific use case. As
it only allows to kick the BSP, not any VCPU, that should be clarified.
Maybe call it KVM_REQUEST_PIC_INJECTION or so. Or allow userspace to
specify the target VCPU, then it's a bit more generic again.

Actually, when looking at the MultiProcessor spec, you will find
multiple models for injecting PIC interrupts into CPU APICs. Just in the
PIC Mode, the BSP is the only possible target. In the other modes, all
APICs can receive PIC interrupts, and either the IOAPIC or the local
APIC's LINT0 configuration decide about the effective target. We should
allow to model all modes, based on userspace decisions.

> 
> Boots and passes the KVM unit tests on intel x86 with the
> PIC/PIT/IOAPIC in userspace (under a non-QEMU VMM). Boots and passes
> the KVM unit tests under normal conditions as well.

Do you plan to provide a reference implementation for an open source
userspace VMM as well, once the kernel side is settled?

> 
> SVM support and device assignment are untested with this feature
> enabled, but testing for both is in the works.
> 
> Compiles for ARM/x86/PPC.
> 
> Signed-off-by: Steve Rutherford <srutherford@google.com>
> ---
>  Documentation/virtual/kvm/api.txt |  9 +++++++
>  arch/x86/include/asm/kvm_host.h   |  1 +
>  arch/x86/kvm/irq.c                |  6 ++++-
>  arch/x86/kvm/lapic.c              |  7 ++++++
>  arch/x86/kvm/lapic.h              |  2 ++
>  arch/x86/kvm/x86.c                | 53 ++++++++++++++++++++++++++++++++++++---
>  include/uapi/linux/kvm.h          |  6 +++++
>  7 files changed, 80 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index dd92996..a650321 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -2993,6 +2993,15 @@ the ioapic nor the pic in the kernel. Also, enables in kernel routing of
>  interrupt requests. Fails if VCPU has already been created, or if the irqchip is
>  already in the kernel.
>  
> +4.97 KVM_REQUEST_LOCAL_INTERRUPT
> +
> +Capability: KVM_CAP_SPLIT_IRQCHIP
> +Type: VM ioctl
> +Parameters: none
> +Returns: 0 on success, -1 on error.
> +
> +Informs the kernel that userspace has a pending external interrupt.
> +
>  
>  5. The kvm_run structure
>  ------------------------
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index b1978f1..602ea70 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -542,6 +542,7 @@ struct kvm_vcpu_arch {
>  
>  	u64 eoi_exit_bitmaps[4];
>  	int pending_ioapic_eoi;
> +	bool pending_external;
>  };
>  
>  struct kvm_lpage_info {
> diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
> index 706e47a..487b5f5 100644
> --- a/arch/x86/kvm/irq.c
> +++ b/arch/x86/kvm/irq.c
> @@ -43,7 +43,11 @@ EXPORT_SYMBOL(kvm_cpu_has_pending_timer);
>   */
>  static int kvm_cpu_has_extint(struct kvm_vcpu *v)
>  {
> -	if (kvm_apic_accept_pic_intr(v))
> +	u8 accept = kvm_apic_accept_pic_intr(v);
> +
> +	if (accept && irqchip_split(v->kvm))
> +		return v->arch.pending_external;
> +	else if (accept)
>  		return pic_irqchip(v->kvm)->output;	/* PIC */
>  	else
>  		return 0;
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 7533b87..9a021f7 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2089,3 +2089,10 @@ void kvm_lapic_init(void)
>  	jump_label_rate_limit(&apic_hw_disabled, HZ);
>  	jump_label_rate_limit(&apic_sw_disabled, HZ);
>  }
> +
> +void kvm_request_local_interrupt(struct kvm_vcpu *vcpu)
> +{
> +	vcpu->arch.pending_external = true;
> +	kvm_make_request(KVM_REQ_EVENT, vcpu);
> +	kvm_vcpu_kick(vcpu);
> +}
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index 71b150c..66bb780 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -63,6 +63,8 @@ int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq,
>  		unsigned long *dest_map);
>  int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type);
>  
> +void kvm_request_local_interrupt(struct kvm_vcpu *vcpu);
> +
>  bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
>  		struct kvm_lapic_irq *irq, int *r, unsigned long *dest_map);
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 6127fe7..b7ceff3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -65,6 +65,8 @@
>  #include <asm/pvclock.h>
>  #include <asm/div64.h>
>  
> +#define GET_VECTOR_FROM_USERSPACE 1
> +
>  #define MAX_IO_MSRS 256
>  #define KVM_MAX_MCE_BANKS 32
>  #define KVM_MCE_CAP_SUPPORTED (MCG_CTL_P | MCG_SER_P)
> @@ -4146,6 +4148,30 @@ split_irqchip_unlock:
>  		mutex_unlock(&kvm->lock);
>  		break;
>  	}
> +	case KVM_REQUEST_LOCAL_INTERRUPT: {
> +		int i;
> +		struct kvm_vcpu *vcpu;
> +		struct kvm_vcpu *bsp_vcpu = NULL;
> +
> +		mutex_lock(&kvm->lock);
> +		r = -EEXIST;

Nitpicking, EEXIST seems confusing. I would go for EINVAL here as well.

> +		if (!irqchip_split(kvm))
> +			goto out;
> +		kvm_for_each_vcpu(i, vcpu, kvm) {
> +			if (kvm_vcpu_is_reset_bsp(vcpu)) {
> +				bsp_vcpu = vcpu;
> +				continue;
> +			}
> +		}
> +		r = -EINVAL;
> +		if (bsp_vcpu == NULL)
> +			goto interrupt_unlock;
> +		kvm_request_local_interrupt(bsp_vcpu);
> +		r = 0;
> +interrupt_unlock:
> +		mutex_unlock(&kvm->lock);
> +		break;
> +	}
>  
>  	default:
>  		r = kvm_vm_ioctl_assigned_device(kvm, ioctl, arg);
> @@ -6123,6 +6149,16 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu)
>  	kvm_x86_ops->update_cr8_intercept(vcpu, tpr, max_irr);
>  }
>  
> +static int pending_userspace_external_intr(struct kvm_vcpu *vcpu)
> +{
> +	if (vcpu->arch.pending_external && kvm_apic_accept_pic_intr(vcpu)) {
> +		vcpu->arch.pending_external = false;
> +		return true;
> +	} else
> +		return false;
> +
> +}
> +
>  static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
>  {
>  	int r;
> @@ -6187,7 +6223,12 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
>  				return r;
>  		}
>  		if (kvm_x86_ops->interrupt_allowed(vcpu)) {
> -			kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu),
> +			if (irqchip_split(vcpu->kvm) &&
> +			    pending_userspace_external_intr(vcpu)) {
> +				return GET_VECTOR_FROM_USERSPACE;
> +			}
> +			kvm_queue_interrupt(vcpu,
> +					    kvm_cpu_get_interrupt(vcpu),
>  					    false);
>  			kvm_x86_ops->set_irq(vcpu);
>  		}
> @@ -6351,13 +6392,19 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	}
>  
>  	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
> +		int event;
>  		kvm_apic_accept_events(vcpu);
>  		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
>  			r = 1;
>  			goto out;
>  		}
> -
> -		if (inject_pending_event(vcpu, req_int_win) != 0)
> +		event = inject_pending_event(vcpu, req_int_win);
> +		if (event == GET_VECTOR_FROM_USERSPACE) {
> +			vcpu->run->exit_reason = KVM_EXIT_GET_EXTINT;
> +			kvm_make_request(KVM_REQ_EVENT, vcpu);
> +			r = 0;
> +			goto out;
> +		} else if (event != 0)
>  			req_immediate_exit = true;
>  		/* enable NMI/IRQ window open exits if needed */
>  		else if (vcpu->arch.nmi_pending)
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 2305948..368e80a 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -184,6 +184,7 @@ struct kvm_s390_skeys {
>  #define KVM_EXIT_SYSTEM_EVENT     24
>  #define KVM_EXIT_S390_STSI        25
>  #define KVM_EXIT_IOAPIC_EOI       26
> +#define KVM_EXIT_GET_EXTINT       27
>  
>  /* For KVM_EXIT_INTERNAL_ERROR */
>  /* Emulate instruction failed. */
> @@ -334,6 +335,10 @@ struct kvm_run {
>  		struct {
>  			__u8 vector;
>  		} eoi;
> +		/* KVM_EXIT_GET_EXTINT */
> +		struct {
> +			__u8 vector;
> +		} extint;
>  		/* Fix the size of the union. */
>  		char padding[256];
>  	};
> @@ -1208,6 +1213,7 @@ struct kvm_s390_ucas_mapping {
>  #define KVM_S390_GET_IRQ_STATE	  _IOW(KVMIO, 0xb6, struct kvm_s390_irq_state)
>  /* Available with KVM_CAP_SPLIT_IRQCHIP */
>  #define KVM_CREATE_SPLIT_IRQCHIP  _IO(KVMIO, 0xb7)
> +#define KVM_REQUEST_LOCAL_INTERRUPT _IO(KVMIO, 0xb8)
>  
>  #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
>  #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
> 

Jan

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