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From:   Zhenyu Ye <yezhenyu2@huawei.com>
Subject: [Question] the check of ioeventfd collision in
 kvm_*assign_ioeventfd_idx
To:     <pbonzini@redhat.com>, <mst@redhat.com>, <gleb@redhat.com>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>, <kvm@vger.kernel.org>,
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        Xiexiangyou <xiexiangyou@huawei.com>, <ghaskins@novell.com>
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Date:   Thu, 30 Jul 2020 22:19:49 +0800
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Hi all,

There are checks of ioeventfd collision in both kvm_assign_ioeventfd_idx()
and kvm_deassign_ioeventfd_idx(), however, with different logic.

In kvm_assign_ioeventfd_idx(), this is done by ioeventfd_check_collision():
---8<---
	if (_p->bus_idx == p->bus_idx &&
	    _p->addr == p->addr &&
	    (!_p->length || !p->length ||
	     (_p->length == p->length &&
	      (_p->wildcard || p->wildcard ||
	       _p->datamatch == p->datamatch))))
		// then we consider the two are the same
---8<---

The logic in kvm_deassign_ioeventfd_idx() is as follows:
---8<---
	if (p->bus_idx != bus_idx ||
	    p->eventfd != eventfd  ||
	    p->addr != args->addr  ||
	    p->length != args->len ||
	    p->wildcard != wildcard)
		continue;

	if (!p->wildcard && p->datamatch != args->datamatch)
		continue;

	// then we consider the two are the same
---8<---

As we can see, there is extra check of p->eventfd in

().  Why we don't check p->eventfd
in kvm_assign_ioeventfd_idx()? Or should we delete this in
kvm_deassign_ioeventfd_idx()?


Thanks,
Zhenyu