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RE: [Xen-devel] A question about SHARE_PFN_WITH_DOMAIN

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] A question about SHARE_PFN_WITH_DOMAIN
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Fri, 13 Jan 2006 17:19:47 +0800
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Thread-topic: [Xen-devel] A question about SHARE_PFN_WITH_DOMAIN
>From: Keir Fraser
>Sent: 2006年1月13日 17:15
>On 13 Jan 2006, at 07:10, Tian, Kevin wrote:
>>> Secondly, there is the subtle and thorny issue of domain destruction.
>>> Xen assume that any domain that has a non-zero reference count has a
>>> valid shared_info, for example.
>> Could you please point out where I can find such assumption in the
>> code?
>Sure. For example, event channel bindings are torn down only when the
>domain refcnt falls to zero. If we freed the shared_info page when dom0
>kills the domain, the refcnt may remain non-zero for some time after
>that (because of mappings of network/block ring pages for example). If
>dom0 tries to notify via an event channel, the evtchn code in Xen will
>happily dereference the dying domU's shared_info pointer which would no
>longer be valid.
>So we cannot free shared_info until domain_destruct(), and if Xen held
>a reference on shared_info then domain_destruct() would never be
>  -- Keir

Clear and make sense.


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