From: "Jan Beulich" <JBeulich@suse.com>
To: Yu Zhang <yu.c.zhang@linux.intel.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: Thu, 16 Jun 2016 03:55:50 -0600 [thread overview]
Message-ID: <576293C602000078000F59AF@prv-mh.provo.novell.com> (raw)
In-Reply-To: <576271CF.8020202@linux.intel.com>
>>> On 16.06.16 at 11:30, <yu.c.zhang@linux.intel.com> wrote:
> On 6/15/2016 6:21 PM, Jan Beulich wrote:
>>>>> On 15.06.16 at 11:50, <george.dunlap@citrix.com> wrote:
>>> On 14/06/16 14:31, Jan Beulich wrote:
>>>>>>> On 14.06.16 at 15:13, <george.dunlap@citrix.com> wrote:
>>>>> On 14/06/16 11:45, Jan Beulich wrote:
>>>>>> Locking is somewhat strange here: You protect against the "set"
>>>>>> counterpart altering state while you retrieve it, but you don't
>>>>>> protect against the returned data becoming stale by the time
>>>>>> the caller can consume it. Is that not a problem? (The most
>>>>>> concerning case would seem to be a race of hvmop_set_mem_type()
>>>>>> with de-registration of the type.)
>>>>> How is that different than calling set_mem_type() first, and then
>>>>> de-registering without first unmapping all the types?
>>>> Didn't we all agree this is something that should be disallowed
>>>> anyway (not that I've seen this implemented, i.e. just being
>>>> reminded of it by your reply)?
>>> I think I suggested it as a good idea, but Paul and Yang both thought it
>>> wasn't necessary. Do you think it should be a requirement?
>> I think things shouldn't be left in a half-adjusted state.
>>
>>> We could have the de-registering operation fail in those circumstances;
>>> but probably a more robust thing to do would be to have Xen go change
>>> all the ioreq_server entires back to ram_rw (since if the caller just
>>> ignores the failure, things are in an even worse state).
>> If that's reasonable to do without undue delay (e.g. by using
>> the usual "recalculate everything" forced to trickle down through
>> the page table levels, then that's as good.
>
> Thanks for your advices, Jan & George.
>
> Previously in the 2nd version, I used p2m_change_entry_type_global() to
> reset the
> outstanding p2m_ioreq_server entries back to p2m_ram_rw asynchronously after
> the de-registration. But we realized later that this approach means we
> can not support
> live migration. And to recalculate the whole p2m table forcefully when
> de-registration
> happens means too much cost.
>
> And further discussion with Paul was that we can leave the
> responsibility to reset p2m type
> to the device model side, and even a device model fails to do so, the
> affected one will only
> be the current VM, neither other VM nor hypervisor will get hurt.
>
> I thought we have reached agreement in the review process of version 2,
> so I removed
> this part from version 3.
In which case I would appreciate the commit message to explain
this (in particular I admit I don't recall why live migration would
be affected by the p2m_change_entry_type_global() approach,
but the request is also so that later readers have at least some
source of information other than searching the mailing list).
> Hah, I guess these 2 #defines are just cloned from similar ones, and I
> did not expected
> they would receive so much comments. Anyway, I admire your preciseness
> and thanks
> for pointing this out. :)
>
> Since the bit number #defines have no special meaning, I'd like to just
> define the flags
> directly:
>
> #define HVMOP_IOREQ_MEM_ACCESS_READ (1u << 0)
> #define HVMOP_IOREQ_MEM_ACCESS_WRITE (1u << 1)
XEN_HVMOP_* then please.
Jan
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next prev parent reply other threads:[~2016-06-16 9:55 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 [this message]
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
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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