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

From: Roman Kagan <rkagan@virtuozzo.com>
To: David Hildenbrand <david@redhat.com>
Cc: kvm@vger.kernel.org, "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Denis V. Lunev" <den@openvz.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>
Subject: Re: [PATCH v5 2/2] kvm: x86: hyperv: guest->host event signaling via eventfd
Date: Wed, 13 Dec 2017 14:44:51 +0300	[thread overview]
Message-ID: <20171213114450.GD18723@rkaganb.sw.ru> (raw)
In-Reply-To: <efeeb454-5fa3-50a7-24d9-a4c289852b21@redhat.com>

On Wed, Dec 13, 2017 at 10:55:02AM +0100, David Hildenbrand wrote:
> 
> > +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."

Ouch.  I wonder what else to map -EFAULT to then...  Looks like
HV_STATUS_INVALID_ALIGNMENT is the most appropriate (as in "The input or
output GPA pointer is not within the bounds of the GPA space.")

Thanks,
Roman.