On 28.04.20 14:46, Paul Durrant wrote:
-----Original Message-----
From: Julien Grall <jul...@xen.org>
Sent: 28 April 2020 11:23
To: Jürgen Groß <jgr...@suse.com>; Paul Durrant <p...@xen.org>;
xen-devel@lists.xenproject.org
Cc: Paul Durrant <pdurr...@amazon.com>; Andrew Cooper
<andrew.coop...@citrix.com>; George Dunlap
<george.dun...@citrix.com>; Ian Jackson <ian.jack...@eu.citrix.com>; Jan Beulich
<jbeul...@suse.com>;
Stefano Stabellini <sstabell...@kernel.org>; Wei Liu <w...@xen.org>
Subject: Re: [PATCH v4] docs/designs: re-work the xenstore migration document...
Hi Juergen,
On 28/04/2020 11:10, Jürgen Groß wrote:
On 28.04.20 11:05, Julien Grall wrote:
-where tx_id is the non-zero identifier values of an open transaction.
+| Field | Description |
+|-----------|---------------------------------------------------|
+| `domid` | The domain-id that owns the shared page |
+| | |
+| `tdomid` | The domain-id that `domid` acts on behalf of if |
+| | it has been subject to an SET_TARGET |
+| | operation [2] or DOMID_INVALID [3] otherwise |
+| | |
+| `flags` | Must be zero |
+| | |
+| `evtchn` | The port number of the interdomain channel used |
+| | by `domid` to communicate with xenstored |
+| | |
+| `mfn` | The MFN of the shared page for a live update or |
+| | ~0 (i.e. all bits set) otherwise |
-### Protocol Extension
+Since the ABI guarantees that entry 1 in `domid`'s grant table will
always
+contain the GFN of the shared page, so for a live update `mfn` can
be used to
+give confidence that `domid` has not been re-cycled during the update.
I am confused, there is no way a XenStored running in an Arm domain
can map the MFN of the shared page. So how is this going to work out?
I guess this will be a MFN for PV guests and a guest PFN else.
If we use Xen terminology (xen/include/xen/mm.h), this would be a GFN.
TBH I'm not sure a GFN would give much confidence about domain recycling as it
would likely be the same for many domains, I think. We really need a UUID.
No, we need a per-host domain value, which is associated with a domain
and which is unique during the life-time of the host.
E.g. a global counter, which is incremented at each domain creation and
stored in struct domain.
Juergen
