From: Yu Zhang <yu.c.zhang@linux.intel.com>
To: Jan Beulich <JBeulich@suse.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>,
George Dunlap <george.dunlap@citrix.com>,
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: Tue, 21 Jun 2016 15:45:03 +0800 [thread overview]
Message-ID: <5768F07F.7010308@linux.intel.com> (raw)
In-Reply-To: <57680DE502000078000F6D43@prv-mh.provo.novell.com>
On 6/20/2016 9:38 PM, Jan Beulich wrote:
>>>> On 20.06.16 at 14:06, <yu.c.zhang@linux.intel.com> wrote:
>> 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.
> Why would it? Changes to p2m_ram_logdirty won't alter
> p2m_ioreq_server entries, and hence changes from it back to
> p2m_ram_rw won't either.
Oh, above example is based on the assumption that resolve_misconfig() is
extended
to handle the p2m_ioreq_server case(see my "Suppose resolve_misconfig()
is modified...").
The code change could be something like below:
@@ -542,10 +542,14 @@ static int resolve_misconfig(struct p2m_domain
*p2m, unsigned long gfn)
- if ( e.recalc && p2m_is_changeable(e.sa_p2mt) )
+ if ( e.recalc )
{
- e.sa_p2mt = p2m_is_logdirty_range(p2m, gfn +
i, gfn + i)
- ? p2m_ram_logdirty : p2m_ram_rw;
+ if ( e.sa_p2mt == p2m_ioreq_server )
+ e.sa_p2mt = p2m_ram_rw;
+ else if ( p2m_is_changeable(e.sa_p2mt) )
+ e.sa_p2mt = p2m_is_logdirty_range(p2m, gfn
+ i, gfn + i)
+ ? p2m_ram_logdirty : p2m_ram_rw;
+
ept_p2m_type_to_flags(p2m, &e, e.sa_p2mt,
e.access);
}
e.recalc = 0;
With changes like this, both p2m types of gfn A and gfn B from above example
would be set to p2m_ram_rw if log dirty is enabled.
So that's what I am worrying - if a user unintentionally typed "xl save"
during
the emulation process , the emulation would fail. We can let the
enable_logdirty()
return false if XenGT is detected, but we still wish to keep the log
dirty feature.
>
> And then - didn't we mean to disable that part of XenGT during
> migration, i.e. temporarily accept the higher performance
> overhead without the p2m_ioreq_server entries? In which case
> flipping everything back to p2m_ram_rw after (completed or
> canceled) migration would be exactly what we want. The (new
> or previous) ioreq server should attach only afterwards, and
> can then freely re-establish any p2m_ioreq_server entries it
> deems necessary.
>
Well, I agree this part of XenGT should be disabled during migration.
But in such
case I think it's device model's job to trigger the p2m type
flipping(i.e. by calling
HVMOP_set_mem_type). And the device model should be notified first when the
migration begins - we may need new patches to do so if XenGT is going to
support
vGPU migration in the future.
Thanks
Yu
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next prev parent reply other threads:[~2016-06-21 7:45 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
2016-06-20 13:38 ` Jan Beulich
2016-06-21 7:45 ` Yu Zhang [this message]
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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