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From: "Yu, Zhang" <yu.c.zhang@linux.intel.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: kevin.tian@intel.com, wei.liu2@citrix.com,
	ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com,
	andrew.cooper3@citrix.com,
	Ian Jackson <Ian.Jackson@eu.citrix.com>,
	xen-devel@lists.xen.org, Paul.Durrant@citrix.com,
	zhiyuan.lv@intel.com, keir@xen.org
Subject: Re: [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges.
Date: Tue, 2 Feb 2016 23:00:21 +0800	[thread overview]
Message-ID: <56B0C485.8070206@linux.intel.com> (raw)
In-Reply-To: <56B0CE8102000078000CD8D4@prv-mh.provo.novell.com>



On 2/2/2016 10:42 PM, Jan Beulich wrote:
>>>> On 02.02.16 at 15:01, <yu.c.zhang@linux.intel.com> wrote:
>> On 2/2/2016 7:12 PM, Jan Beulich wrote:
>>>>>> On 02.02.16 at 11:56, <yu.c.zhang@linux.intel.com> wrote:
>>>> I understand your concern, and to be honest, I do not think
>>>> this is an optimal solution. But I also have no better idea
>>>> in mind.  :(
>>>> Another option may be: instead of opening this parameter to
>>>> the tool stack, we use a XenGT flag, which set the rangeset
>>>> limit to a default value. But like I said, this default value
>>>> may not always work on future XenGT platforms.
>>>
>>> Assuming that you think of something set e.g. by hypervisor
>>> command line option: How would that work? I.e. how would
>>> that limit the resource use for all VMs not using XenGT? Or if
>>> you mean a flag settable in the domain config - how would you
>>> avoid a malicious admin to set this flag for all the VMs created
>>> in the controlled partition of the system?
>>
>> Well, I am not satisfied with this new parameter, because:
>> 1> exposing an option like max_wp_ram_ranges to the user seems too
>> detailed;
>> 2> but if not, using a XenGT flag means it would be hard for hypervisor
>> to find a default value which can work in all situations theoretically,
>> although in practice, 8K is already a big enough one.
>>
>> However, as to the security concern you raised, I can not fully
>> understand. :) E.g. I believe a malicious admin can also breach the
>> system even without this patch. This argument may not be convincing to
>> you, but as to this specific case, even if an admin set XenGT flag to
>> all VMs, what harm will this action do? It only means the ioreq server
>> can at most allocate 8K ranges, will that consume all the Xen heaps,
>> especially for 64 bit Xen?
>
> First of all so far you meant to set a limit of 4G, which - taking a
> handful of domains - if fully used would take even a mid-size
> host out of memory. And then you have to consider bad effects
> resulting from Xen itself not normally having a lot of memory left
> (especially when "dom0_mem=" is not forcing most of the memory
> to be in Xen's hands), which may mean that one domain
> exhausting Xen's memory can affect another domain if Xen can't
> allocate memory it needs to support that other domain, in the
> worst case leading to a domain crash. And this all is still leaving
> aside Xen's own health...
>

Thanks, Jan.
The limit of 4G is to avoid the data missing from uint64 to uint32
assignment. And I can accept the 8K limit for XenGT in practice.
After all, it is vGPU page tables we are trying to trap and emulate,
not normal page frames.

And I guess the reason that one domain exhausting Xen's memory can
affect another domain is because rangeset uses Xen heap, instead of the
per-domain memory. So what about we use a 8K limit by now for XenGT,
and in the future, if a per-domain memory allocation solution for
rangeset is ready, we do need to limit the rangeset size. Does this
sounds more acceptable?

B.R.
Yu

  reply	other threads:[~2016-02-02 15:00 UTC|newest]

Thread overview: 109+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-29 10:45 [PATCH v12 0/3] Refactor ioreq server for better performance Yu Zhang
2016-01-29 10:45 ` [PATCH v12 1/3] Refactor rangeset structure " Yu Zhang
2016-01-29 10:45 ` [PATCH v12 2/3] Differentiate IO/mem resources tracked by ioreq server Yu Zhang
2016-01-29 10:45 ` [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges Yu Zhang
2016-01-29 16:33   ` Jan Beulich
2016-01-30 14:38     ` Yu, Zhang
2016-02-01  7:52       ` Jan Beulich
2016-02-01 12:02         ` Wei Liu
2016-02-01 12:15           ` Jan Beulich
2016-02-01 12:49             ` Wei Liu
2016-02-01 13:07               ` Jan Beulich
2016-02-01 15:14                 ` Yu, Zhang
2016-02-01 16:16                   ` Jan Beulich
2016-02-01 16:33                     ` Yu, Zhang
2016-02-01 16:19                   ` Yu, Zhang
2016-02-01 16:35                     ` Jan Beulich
2016-02-01 16:37                       ` Yu, Zhang
2016-02-01 17:05                         ` Ian Jackson
2016-02-02  8:04                           ` Yu, Zhang
2016-02-02 11:51                             ` Wei Liu
2016-02-02 13:56                               ` Yu, Zhang
2016-02-02 10:32                           ` Jan Beulich
2016-02-02 10:56                             ` Yu, Zhang
2016-02-02 11:12                               ` Jan Beulich
2016-02-02 14:01                                 ` Yu, Zhang
2016-02-02 14:42                                   ` Jan Beulich
2016-02-02 15:00                                     ` Yu, Zhang [this message]
2016-02-02 15:21                                       ` Jan Beulich
2016-02-02 15:19                                         ` Yu, Zhang
2016-02-03  7:10                                         ` Yu, Zhang
2016-02-03  8:32                                           ` Jan Beulich
2016-02-03 12:20                                             ` Paul Durrant
2016-02-03 12:35                                               ` Jan Beulich
2016-02-03 12:50                                                 ` Paul Durrant
2016-02-03 13:00                                                   ` Jan Beulich
2016-02-03 13:07                                                     ` Paul Durrant
2016-02-03 13:17                                                       ` Jan Beulich
2016-02-03 13:18                                                         ` Paul Durrant
2016-02-03 14:43                                                           ` Ian Jackson
2016-02-03 15:10                                                             ` Paul Durrant
2016-02-03 17:50                                                               ` George Dunlap
2016-02-04  8:50                                                                 ` Yu, Zhang
2016-02-03 17:41                                                             ` George Dunlap
2016-02-03 18:21                                                               ` George Dunlap
2016-02-03 18:26                                                                 ` George Dunlap
2016-02-03 18:39                                                                 ` Andrew Cooper
2016-02-03 19:12                                                                   ` George Dunlap
2016-02-04  8:51                                                                     ` Yu, Zhang
2016-02-04 10:49                                                                       ` George Dunlap
2016-02-04 11:08                                                                         ` Ian Campbell
2016-02-04 11:19                                                                           ` Ian Campbell
2016-02-04  8:50                                                                 ` Yu, Zhang
2016-02-04  9:28                                                                   ` Paul Durrant
2016-02-04  9:38                                                                     ` Yu, Zhang
2016-02-04  9:49                                                                       ` Paul Durrant
2016-02-04 10:34                                                                       ` Jan Beulich
2016-02-04 13:33                                                                         ` Ian Jackson
2016-02-04 13:47                                                                           ` Paul Durrant
2016-02-04 14:12                                                                             ` Jan Beulich
2016-02-04 14:25                                                                               ` Paul Durrant
2016-02-04 15:06                                                                                 ` Ian Jackson
2016-02-04 15:51                                                                                   ` Paul Durrant
2016-02-05  3:47                                                                                     ` Tian, Kevin
2016-02-05  3:35                                                                               ` Tian, Kevin
2016-02-04 14:08                                                                           ` Jan Beulich
2016-02-04 17:12                                                                             ` George Dunlap
2016-02-05  4:18                                                                               ` Tian, Kevin
2016-02-05  8:41                                                                                 ` Yu, Zhang
2016-02-05  8:32                                                                               ` Jan Beulich
2016-02-05  9:24                                                                                 ` Paul Durrant
2016-02-05 10:41                                                                                   ` Jan Beulich
2016-02-05 11:14                                                                                   ` George Dunlap
2016-02-05 11:24                                                                                     ` Paul Durrant
2016-02-16  7:22                                                                                       ` Tian, Kevin
2016-02-16  8:50                                                                                         ` Paul Durrant
2016-02-16 10:33                                                                                           ` Jan Beulich
2016-02-16 11:11                                                                                             ` Paul Durrant
2016-02-17  3:18                                                                                               ` Tian, Kevin
2016-02-17  8:58                                                                                                 ` Paul Durrant
2016-02-17  9:32                                                                                                   ` Jan Beulich
2016-02-17  9:58                                                                                                   ` Tian, Kevin
2016-02-17 10:03                                                                                                     ` Paul Durrant
2016-02-17 10:22                                                                                                     ` Jan Beulich
2016-02-17 10:24                                                                                                       ` Paul Durrant
2016-02-17 10:25                                                                                                         ` Tian, Kevin
2016-02-17 11:01                                                                                                       ` George Dunlap
2016-02-17 11:12                                                                                                         ` Paul Durrant
2016-02-22 15:56                                                                                                           ` George Dunlap
2016-02-22 16:02                                                                                                             ` Paul Durrant
2016-02-22 16:45                                                                                                               ` George Dunlap
2016-02-22 17:01                                                                                                                 ` Paul Durrant
2016-02-22 17:23                                                                                                                   ` George Dunlap
2016-02-22 17:34                                                                                                                     ` Paul Durrant
2016-02-05  8:41                                                                               ` Yu, Zhang
2016-02-04 11:06                                                                       ` George Dunlap
2016-02-05  2:01                                                                         ` Zhiyuan Lv
2016-02-05  3:44                                                                           ` Tian, Kevin
2016-02-05  8:38                                                                             ` Jan Beulich
2016-02-05 11:05                                                                             ` George Dunlap
2016-02-05 15:13                                                                               ` Zhiyuan Lv
2016-02-05 20:14                                                                                 ` George Dunlap
2016-02-05  8:40                                                                         ` Yu, Zhang
2016-02-04 10:06                                                               ` Ian Campbell
2016-02-05  3:31                                                                 ` Tian, Kevin
2016-02-02 11:31                             ` Andrew Cooper
2016-02-02 11:43                               ` Jan Beulich
2016-02-02 14:20                                 ` Andrew Cooper
2016-02-01 11:57   ` Wei Liu
2016-02-01 15:15     ` Yu, Zhang

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