From: "Roger Pau Monné" <roger.pau@citrix.com>
To: xen-devel@lists.xenproject.org
Cc: George.Dunlap@eu.citrix.com, keir@xen.org, tim@xen.org,
JBeulich@suse.com
Subject: P2M aliasing check
Date: Fri, 1 Apr 2016 19:18:16 +0200 [thread overview]
Message-ID: <alpine.OSX.2.20.1604011908340.9476@mac> (raw)
Hello,
While trying to get hotplug scripts to work on FreeBSD, I've realized that
there's a check in the P2M code that prevents having multiple gfn pointing
to the same mfn. The check in question is performed at
guest_physmap_add_entry, and it means that the existing gfn -> mfn is
removed and the new one is added, leaving the previous gfn without a valid
mfn.
This is a problem specially for PVH Dom0, since it means local-attach of
virtual disk devices lead to a crash of the Dom0. This happens because
Dom0 is sharing a grant with itself, and then the original gfn -> mfn
assignment gets destroyed in favor of the new one created by mapping the
grant reference.
I would like to understand the reason why this check is in place, and why
aliased gfn -> mfn mappings are not permitted. This is a different behavior
as compared to PV guests, where multiple VA -> mfn mappings are permitted.
Roger.
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next reply other threads:[~2016-04-01 17:19 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-01 17:18 Roger Pau Monné [this message]
2016-04-04 8:23 ` P2M aliasing check Jan Beulich
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