From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olaf Hering <olaf@aepfle.de>
Subject: xenstore index reset in xb_init_comms breaks domU kdump
Date: Wed, 26 Jan 2011 15:00:44 +0100
Message-ID: <20110126140043.GA27631@aepfle.de>
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To: Keir Fraser <keir@xen.org>
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Keir,

in the commit below a reset of the rsp_cons/rsp_prod index was added.
http://xenbits.xen.org/staging/xen-unstable.hg?rev/1ec0d322402e

Is this reset really required for save/restore? I have not tried it, but
I would assume a restored guest would get an empty page to work with.
Also:
Could a guest be saved when its in the middle of a xenstore operation?

The reset breaks the xenstore interface in a crashed domU kernel. If the
crash kernel boots, it tries to operate on the new rsp_* index. But this
contains garbage, process_msg() tries to use the data as 'struct
xsd_sockmsg', and kmalloc() fails.
If I remove the rsp_cons/rsp_prod reset in xb_init_comms(), the PV
drivers in the crash kernel can connect to xenstore.

Should the fixup code be removed, or is it essential for save/restore?


Olaf