linux-kernel - Re: [Question] the check of ioeventfd collision in kvm_*assign_ioeventfd

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Message-ID: <cffcf9e1-6675-6815-ccfc-f48497ade818@redhat.com>
Date:   Fri, 31 Jul 2020 08:44:56 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Zhenyu Ye <yezhenyu2@...wei.com>
Cc:     "S. Tsirkin, Michael" <mst@...hat.com>, gleb@...hat.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        Xiexiangyou <xiexiangyou@...wei.com>
Subject: Re: [Question] the check of ioeventfd collision in
 kvm_*assign_ioeventfd_idx

On 31/07/20 08:39, Zhenyu Ye wrote:
> On 2020/7/31 2:03, Paolo Bonzini wrote:
>> Yes, I think it's not needed. Probably the deassign check can be turned into an assertion?
>>
>> Paolo
>>
> 
> I think we can do this in the same function, and turnt he check of
> p->eventfd into assertion in kvm_deassign_ioeventfd_idx(). Just like:
> 
> ---8<---
> static inline struct _ioeventfd *
> get_ioeventfd(struct kvm *kvm, enum kvm_bus bus_idx,
>               struct kvm_ioeventfd *args)
> {
>         static struct _ioeventfd *_p;
>         bool wildcard = !(args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH);
> 
>         list_for_each_entry(_p, &kvm->ioeventfds, list)
>                 if (_p->bus_idx == bus_idx &&
>                     _p->addr == args->addr &&
>                     (!_p->length || !args->len ||
>                      (_p->length == args->len &&
>                       (_p->wildcard || wildcard ||
>                        _p->datamatch == args->datamatch))))
>                         return _p;
> 
>         return NULL;
> }
> 
> kvm_deassign_ioeventfd_idx() {
> 	...
> 	p = get_ioeventfd(kvm, bus_idx, args);
> 	if (p) {
> 		assert(p->eventfd == eventfd);
> 		...
> 	}
> 
> ---8<----
> 
> This may be easier to understand (keep the same logic in assign/deassign).

I think you should also warn if:

1) p->length != args->len

2) p->wildcard != args->wildcard if p->length

3) p->datamatch != args->datamatch if p->length && !p->wildcard

but yeah it sounds like a plan.

Paolo