Re: [PATCH v5 2/2] kvm: x86: hyperv: guest->host event signaling via eventfd

[David Hildenbrand <david@xxxxxxxxxx>]

> +static u16 kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, bool fast, u64 param)
> +{
> +	u16 ret;
> +	u32 conn_id, flag_no;
> +	int idx;
> +	struct eventfd_ctx *eventfd;
> +
> +	if (unlikely(!fast)) {
> +		gpa_t gpa = param;
> +
> +		if ((gpa & (__alignof__(param) - 1)) ||
> +		    offset_in_page(gpa) + sizeof(param) > PAGE_SIZE)
> +			return HV_STATUS_INVALID_ALIGNMENT;
> +
> +		idx = srcu_read_lock(&vcpu->kvm->srcu);
> +		ret = kvm_vcpu_read_guest(vcpu, gpa, &param, sizeof(param));
> +		srcu_read_unlock(&vcpu->kvm->srcu, idx);
> +
> +		if (ret < 0)
> +			return HV_STATUS_INSUFFICIENT_MEMORY;

"... event flags do not require any buffer allocation or queuing within
the hypervisor, so HvSignalEvent will never fail due to insufficient
resources."


> +	}
> +
> +	/*
> +	 * the signaled event number is made up of a 24bit "connection id" and
> +	 * a 16bit "flag number"; on the hypervisor side it's only their sum
> +	 * that matters

-- 

Thanks,

David / dhildenb