From: Yu Zhang <yu.c.zhang@linux.intel.com>
To: Jan Beulich <JBeulich@suse.com>,
George Dunlap <george.dunlap@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
George Dunlap <george.dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Tim Deegan <tim@xen.org>,
xen-devel@lists.xen.org, Paul Durrant <paul.durrant@citrix.com>,
zhiyuan.lv@intel.com, JunNakajima <jun.nakajima@intel.com>
Subject: Re: [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.
Date: Mon, 20 Jun 2016 20:06:56 +0800 [thread overview]
Message-ID: <5767DC60.5010703@linux.intel.com> (raw)
In-Reply-To: <5767ED8D02000078000F6A0F@prv-mh.provo.novell.com>
On 6/20/2016 7:20 PM, Jan Beulich wrote:
>>>> On 20.06.16 at 13:06, <yu.c.zhang@linux.intel.com> wrote:
>> On 6/20/2016 6:45 PM, Jan Beulich wrote:
>>>>>> On 20.06.16 at 12:30, <yu.c.zhang@linux.intel.com> wrote:
>>>> On 6/20/2016 6:10 PM, George Dunlap wrote:
>>>>> On 20/06/16 10:03, Yu Zhang wrote:
>>>>>> So one solution is to disallow the log dirty feature in XenGT, i.e. just
>>>>>> return failure when enable_logdirty()
>>>>>> is called in toolstack. But I'm afraid this will restrict XenGT's future
>>>>>> live migration feature.
>>>>> I don't understand this -- you can return -EBUSY if live migration is
>>>>> attempted while there are outstanding ioreq_server entries for the time
>>>>> being, and at some point in the future when this actually works, you can
>>>>> return success.
>>>>>
>>>> Well, the problem is we cannot easily tell if there's any outstanding
>>>> p2m_ioreq_server entries.
>>> That's easy to address: Keep a running count.
>> Oh, sorry, let me try to clarify: here by "outstanding p2m_ioreq_server
>> entries", I mean the
>> entries with p2m_ioreq_server type which have not been set back to
>> p2m_ram_rw by device
>> model when the ioreq server detaches. But with asynchronous resetting,
>> we can not differentiate
>> these entries with the normal write protected ones which also have the
>> p2m_ioreq_server set.
> I guess I'm missing something here, because I can't see why we
> can't distinguish them (and also can't arrange for that).
>
Because both have the same p2m type and access rights.
Sorry, it's my duty to explain this more clearly, but I just realized
it's hard to describe. :)
Let me try to elaborate this with an example:
Suppose resolve_misconfig() is modified to change all p2m_ioreq_server
entries(which also
have e.recalc flag turned on) back to p2m_ram_rw. And suppose we have
ioreq server 1, which
emulates gfn A, and ioreq server 2 which emulates gfn B:
1> At the beginning, ioreq server 1 is attached to p2m_ioreq_server, and
gfn A is write protected
by setting it to p2m_ioreq_server;
2> ioreq server 1 is detached from p2m_ioreq_server, left gfn A's p2m
type unchanged;
3> After the detachment of ioreq server 1,
p2m_change_entry_type_global() is called, all ept
entries are invalidated;
4> Later, ioreq server 2 is attached to p2m_ioreq_server;
5> Gfn B is set to p2m_ioreq_server, although its corresponding ept
entry was invalidated,
ept_set_entry() will trigger resolve_misconfig(), which will set the p2m
type of gfn B back to
p2m_ram_rw;
6> ept_set_entry() will set gfn B's p2m type to p2m_ioreq_server next;
And now, we have two
ept entries with p2m_ioreq_server type - gfn A's and gfn B's.
With no live migration, things could work fine - later accesses to gfn A
will ultimately change
its type back to p2m_ram_rw.
However, if live migration is started(all pte entries invalidated
again), resolve_misconfig() would
change both gfn A's and gfn B's p2m type back to p2m_ram_rw, which means
the emulation of
gfn B would fail.
I tried to further extend the log dirty logic to solve this conflict,
but failed, because we do not
know for sure when the resetting of gfn A will be performed and the code
can not easily tell
the different expectations for gfn A and gfn B because they both have
the same p2m type
and access rights.
Hope you can understand this problem and I would be very appreciated if
you have any suggestion.
Anyway, thanks for your patience! :)
Thanks
yu
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next prev parent reply other threads:[~2016-06-20 12:06 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-19 9:05 [PATCH v4 0/3] x86/ioreq server: Introduce HVMMEM_ioreq_server mem type Yu Zhang
2016-05-19 9:05 ` [PATCH v4 1/3] x86/ioreq server: Rename p2m_mmio_write_dm to p2m_ioreq_server Yu Zhang
2016-06-14 10:04 ` Jan Beulich
2016-06-14 13:14 ` George Dunlap
2016-06-15 10:51 ` Yu Zhang
2016-05-19 9:05 ` [PATCH v4 2/3] x86/ioreq server: Add new functions to get/set memory types Yu Zhang
2016-05-19 9:05 ` [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server Yu Zhang
2016-06-14 10:45 ` Jan Beulich
2016-06-14 13:13 ` George Dunlap
2016-06-14 13:31 ` Jan Beulich
2016-06-15 9:50 ` George Dunlap
2016-06-15 10:21 ` Jan Beulich
2016-06-15 11:28 ` George Dunlap
2016-06-16 9:30 ` Yu Zhang
2016-06-16 9:55 ` Jan Beulich
2016-06-17 10:17 ` George Dunlap
2016-06-20 9:03 ` Yu Zhang
2016-06-20 10:10 ` George Dunlap
2016-06-20 10:25 ` Jan Beulich
2016-06-20 10:32 ` George Dunlap
2016-06-20 10:55 ` Jan Beulich
2016-06-20 11:28 ` Yu Zhang
2016-06-20 13:13 ` George Dunlap
2016-06-21 7:42 ` Yu Zhang
2016-06-20 10:30 ` Yu Zhang
2016-06-20 10:43 ` George Dunlap
2016-06-20 10:45 ` Jan Beulich
2016-06-20 11:06 ` Yu Zhang
2016-06-20 11:20 ` Jan Beulich
2016-06-20 12:06 ` Yu Zhang [this message]
2016-06-20 13:38 ` Jan Beulich
2016-06-21 7:45 ` Yu Zhang
2016-06-21 8:22 ` Jan Beulich
2016-06-21 9:16 ` Yu Zhang
2016-06-21 9:47 ` Jan Beulich
2016-06-21 10:00 ` Yu Zhang
2016-06-21 14:38 ` George Dunlap
2016-06-22 6:39 ` Jan Beulich
2016-06-22 8:38 ` Yu Zhang
2016-06-22 9:11 ` Jan Beulich
2016-06-22 9:16 ` George Dunlap
2016-06-22 9:29 ` Jan Beulich
2016-06-22 9:47 ` George Dunlap
2016-06-22 10:07 ` Yu Zhang
2016-06-22 11:33 ` George Dunlap
2016-06-23 7:37 ` Yu Zhang
2016-06-23 10:33 ` George Dunlap
2016-06-24 4:16 ` Yu Zhang
2016-06-24 6:12 ` Jan Beulich
2016-06-24 7:12 ` Yu Zhang
2016-06-24 8:01 ` Jan Beulich
2016-06-24 9:57 ` Yu Zhang
2016-06-24 10:27 ` Jan Beulich
2016-06-22 10:10 ` Jan Beulich
2016-06-22 10:15 ` George Dunlap
2016-06-22 11:50 ` Jan Beulich
2016-06-15 10:52 ` Yu Zhang
2016-06-15 12:26 ` Jan Beulich
2016-06-16 9:32 ` Yu Zhang
2016-06-16 10:02 ` Jan Beulich
2016-06-16 11:18 ` Yu Zhang
2016-06-16 12:43 ` Jan Beulich
2016-06-20 9:05 ` Yu Zhang
2016-06-14 13:14 ` George Dunlap
2016-05-27 7:52 ` [PATCH v4 0/3] x86/ioreq server: Introduce HVMMEM_ioreq_server mem type Zhang, Yu C
2016-05-27 10:00 ` Jan Beulich
2016-05-27 9:51 ` Zhang, Yu C
2016-05-27 10:02 ` George Dunlap
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