Re: [PATCH v4 14/21] KVM: arm64: Support SDEI_EVENT_{COMPLETE, COMPLETE_AND_RESUME} hypercall

[Gavin Shan <gshan@xxxxxxxxxx>]

Hi Eric,

On 11/10/21 6:58 PM, Eric Auger wrote:
> On 8/15/21 2:13 AM, Gavin Shan wrote:
> > This supports SDEI_EVENT_{COMPLETE, COMPLETE_AND_RESUME} hypercall.
> > They are used by the guest to notify the completion of the SDEI
> > event in the handler. The registers are changed according to the
> > SDEI specification as below:
> >
> >     * x0 - x17, PC and PState are restored to what values we had in
> >       the interrupted context.
> >
> >     * If it's SDEI_EVENT_COMPLETE_AND_RESUME hypercall, IRQ exception
> >       is injected.
> >
> > Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
> > ---
> >   arch/arm64/include/asm/kvm_emulate.h |  1 +
> >   arch/arm64/include/asm/kvm_host.h    |  1 +
> >   arch/arm64/kvm/hyp/exception.c       |  7 +++
> >   arch/arm64/kvm/inject_fault.c        | 27 ++++++++++
> >   arch/arm64/kvm/sdei.c                | 75 ++++++++++++++++++++++++++++
> >   5 files changed, 111 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> > index fd418955e31e..923b4d08ea9a 100644
> > --- a/arch/arm64/include/asm/kvm_emulate.h
> > +++ b/arch/arm64/include/asm/kvm_emulate.h
> > @@ -37,6 +37,7 @@ bool kvm_condition_valid32(const struct kvm_vcpu *vcpu);
> >   void kvm_skip_instr32(struct kvm_vcpu *vcpu);
> >   
> >   void kvm_inject_undefined(struct kvm_vcpu *vcpu);
> > +void kvm_inject_irq(struct kvm_vcpu *vcpu);
> >   void kvm_inject_vabt(struct kvm_vcpu *vcpu);
> >   void kvm_inject_dabt(struct kvm_vcpu *vcpu, unsigned long addr);
> >   void kvm_inject_pabt(struct kvm_vcpu *vcpu, unsigned long addr);
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 46f363aa6524..1824f7e1f9ab 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -437,6 +437,7 @@ struct kvm_vcpu_arch {
> >   #define KVM_ARM64_EXCEPT_AA32_UND	(0 << 9)
> >   #define KVM_ARM64_EXCEPT_AA32_IABT	(1 << 9)
> >   #define KVM_ARM64_EXCEPT_AA32_DABT	(2 << 9)
> > +#define KVM_ARM64_EXCEPT_AA32_IRQ	(3 << 9)
> >   /* For AArch64: */
> >   #define KVM_ARM64_EXCEPT_AA64_ELx_SYNC	(0 << 9)
> >   #define KVM_ARM64_EXCEPT_AA64_ELx_IRQ	(1 << 9)
> > diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
> > index 0418399e0a20..ef458207d152 100644
> > --- a/arch/arm64/kvm/hyp/exception.c
> > +++ b/arch/arm64/kvm/hyp/exception.c
> > @@ -310,6 +310,9 @@ static void kvm_inject_exception(struct kvm_vcpu *vcpu)
> >   		case KVM_ARM64_EXCEPT_AA32_DABT:
> >   			enter_exception32(vcpu, PSR_AA32_MODE_ABT, 16);
> >   			break;
> > +		case KVM_ARM64_EXCEPT_AA32_IRQ:
> > +			enter_exception32(vcpu, PSR_AA32_MODE_IRQ, 4);
> > +			break;
> >   		default:
> >   			/* Err... */
> >   			break;
> > @@ -320,6 +323,10 @@ static void kvm_inject_exception(struct kvm_vcpu *vcpu)
> >   		      KVM_ARM64_EXCEPT_AA64_EL1):
> >   			enter_exception64(vcpu, PSR_MODE_EL1h, except_type_sync);
> >   			break;
> > +		case (KVM_ARM64_EXCEPT_AA64_ELx_IRQ |
> > +		      KVM_ARM64_EXCEPT_AA64_EL1):
> > +			enter_exception64(vcpu, PSR_MODE_EL1h, except_type_irq);
> > +			break;
> >   		default:
> >   			/*
> >   			 * Only EL1_SYNC makes sense so far, EL2_{SYNC,IRQ}
> > diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
> > index b47df73e98d7..3a8c55867d2f 100644
> > --- a/arch/arm64/kvm/inject_fault.c
> > +++ b/arch/arm64/kvm/inject_fault.c
> > @@ -66,6 +66,13 @@ static void inject_undef64(struct kvm_vcpu *vcpu)
> >   	vcpu_write_sys_reg(vcpu, esr, ESR_EL1);
> >   }
> >   
> > +static void inject_irq64(struct kvm_vcpu *vcpu)
> > +{
> > +	vcpu->arch.flags |= (KVM_ARM64_EXCEPT_AA64_EL1     |
> > +			     KVM_ARM64_EXCEPT_AA64_ELx_IRQ |
> > +			     KVM_ARM64_PENDING_EXCEPTION);
> > +}
> > +
> >   #define DFSR_FSC_EXTABT_LPAE	0x10
> >   #define DFSR_FSC_EXTABT_nLPAE	0x08
> >   #define DFSR_LPAE		BIT(9)
> > @@ -77,6 +84,12 @@ static void inject_undef32(struct kvm_vcpu *vcpu)
> >   			     KVM_ARM64_PENDING_EXCEPTION);
> >   }
> >   
> > +static void inject_irq32(struct kvm_vcpu *vcpu)
> > +{
> > +	vcpu->arch.flags |= (KVM_ARM64_EXCEPT_AA32_IRQ |
> > +			     KVM_ARM64_PENDING_EXCEPTION);
> > +}
> > +
> >   /*
> >    * Modelled after TakeDataAbortException() and TakePrefetchAbortException
> >    * pseudocode.
> > @@ -160,6 +173,20 @@ void kvm_inject_undefined(struct kvm_vcpu *vcpu)
> >   		inject_undef64(vcpu);
> >   }
> >   
> > +/**
> > + * kvm_inject_irq - inject an IRQ into the guest
> > + *
> > + * It is assumed that this code is called from the VCPU thread and that the
> > + * VCPU therefore is not currently executing guest code.
> > + */
> > +void kvm_inject_irq(struct kvm_vcpu *vcpu)
> > +{
> > +	if (vcpu_el1_is_32bit(vcpu))
> > +		inject_irq32(vcpu);
> > +	else
> > +		inject_irq64(vcpu);
> > +}
> > +
> >   void kvm_set_sei_esr(struct kvm_vcpu *vcpu, u64 esr)
> >   {
> >   	vcpu_set_vsesr(vcpu, esr & ESR_ELx_ISS_MASK);
> > diff --git a/arch/arm64/kvm/sdei.c b/arch/arm64/kvm/sdei.c
> > index b5d6d1ed3858..1e8e213c9d70 100644
> > --- a/arch/arm64/kvm/sdei.c
> > +++ b/arch/arm64/kvm/sdei.c
> > @@ -308,6 +308,75 @@ static unsigned long kvm_sdei_hypercall_context(struct kvm_vcpu *vcpu)
> >   	return ret;
> >   }
> >   
> > +static unsigned long kvm_sdei_hypercall_complete(struct kvm_vcpu *vcpu,
> > +						 bool resume)
> > +{
> > +	struct kvm *kvm = vcpu->kvm;
> > +	struct kvm_sdei_kvm *ksdei = kvm->arch.sdei;
> > +	struct kvm_sdei_vcpu *vsdei = vcpu->arch.sdei;
> > +	struct kvm_sdei_kvm_event *kske = NULL;
> > +	struct kvm_sdei_vcpu_event *ksve = NULL;
> > +	struct kvm_sdei_vcpu_regs *regs;
> > +	unsigned long ret = SDEI_SUCCESS;
> for the RESUME you never seem to read resume_addr arg? How does it work?
> I don't get the irq injection path. Please could you explain?

The guest kernel uses COMPLETE and COMPLETE_AND_RESUME hypercalls to notify the
SDEI event has been acknoledged by it. The difference between them is COMPLETE_AND_RESUME
fires the pending interrupts, but COMPLETE doesn't.

> > +	int index;
> > +
> > +	/* Sanity check */
> > +	if (!(ksdei && vsdei)) {
> > +		ret = SDEI_NOT_SUPPORTED;
> > +		goto out;
> > +	}
> > +
> > +	spin_lock(&vsdei->lock);
> > +	if (vsdei->critical_event) {
> > +		ksve = vsdei->critical_event;
> > +		regs = &vsdei->state.critical_regs;
> > +		vsdei->critical_event = NULL;
> > +		vsdei->state.critical_num = KVM_SDEI_INVALID_NUM;
> > +	} else if (vsdei->normal_event) {
> > +		ksve = vsdei->normal_event;
> > +		regs = &vsdei->state.normal_regs;
> > +		vsdei->normal_event = NULL;
> > +		vsdei->state.normal_num = KVM_SDEI_INVALID_NUM;
> > +	} else {
> > +		ret = SDEI_DENIED;
> > +		goto unlock;
> > +	}
> > +
> > +	/* Restore registers: x0 -> x17, PC, PState */
> > +	for (index = 0; index < ARRAY_SIZE(regs->regs); index++)
> > +		vcpu_set_reg(vcpu, index, regs->regs[index]);
> > +
> > +	*vcpu_cpsr(vcpu) = regs->pstate;
> > +	*vcpu_pc(vcpu) = regs->pc;
> > +
> > +	/* Inject interrupt if needed */
> > +	if (resume)
> > +		kvm_inject_irq(vcpu);
> > +
> > +	/*
> > +	 * Update state. We needn't take lock in order to update the KVM
> > +	 * event state as it's not destroyed because of the reference
> > +	 * count.
> > +	 */
> > +	kske = ksve->kske;
> > +	ksve->state.refcount--;
> > +	kske->state.refcount--;
> why double --?

On each SDEI event is queued for delivery, both reference count are increased. I guess
it's a bit confusing. I will change in next revision:

ksve->state.refcount: Increased on each SDEI event is queued for delivered
kske->state.refcount: Increased on each @ksve is created


> > +	if (!ksve->state.refcount) {
> why not using a struct kref directly?

The reason is kref isn't friendly to userspace. This field (@refcount) needs to be
migrated :)

> > +		list_del(&ksve->link);
> > +		kfree(ksve);
> > +	}
> > +
> > +	/* Make another request if there is pending event */
> > +	if (!(list_empty(&vsdei->critical_events) &&
> > +	      list_empty(&vsdei->normal_events)))
> > +		kvm_make_request(KVM_REQ_SDEI, vcpu);
> > +
> > +unlock:
> > +	spin_unlock(&vsdei->lock);
> > +out:
> > +	return ret;
> > +}
> > +
> >   static unsigned long kvm_sdei_hypercall_unregister(struct kvm_vcpu *vcpu)
> >   {
> >   	struct kvm *kvm = vcpu->kvm;
> > @@ -628,7 +697,13 @@ int kvm_sdei_hypercall(struct kvm_vcpu *vcpu)
> >   		ret = kvm_sdei_hypercall_context(vcpu);
> >   		break;
> >   	case SDEI_1_0_FN_SDEI_EVENT_COMPLETE:
> > +		has_result = false;
> > +		ret = kvm_sdei_hypercall_complete(vcpu, false);
> > +		break;
> >   	case SDEI_1_0_FN_SDEI_EVENT_COMPLETE_AND_RESUME:
> > +		has_result = false;
> > +		ret = kvm_sdei_hypercall_complete(vcpu, true);
> > +		break;
> >   	case SDEI_1_0_FN_SDEI_EVENT_UNREGISTER:
> >   		ret = kvm_sdei_hypercall_unregister(vcpu);
> >   		break;

Thanks,
Gavin

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