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Re: [Xen-devel] Question about MDS mitigation
- To: "wencongyang (A)" <wencongyang2@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 16 May 2019 08:58:54 +0100
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- Cc: gaowanlong <gaowanlong@xxxxxxxxxx>, "Liujinsong \(Paul\)" <liu.jinsong@xxxxxxxxxx>, Huangzhichao <huangzhichao@xxxxxxxxxx>, "Chentao \(Boby\)" <boby.chen@xxxxxxxxxx>, guijianfeng <guijianfeng@xxxxxxxxxx>
- Delivery-date: Thu, 16 May 2019 07:59:09 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 16/05/2019 08:56, wencongyang (A) wrote:
>
> On 2019/5/16 15:38, Andrew Cooper wrote:
>> On 16/05/2019 03:46, wencongyang (A) wrote:
>>> Hi all
>>>
>>> Fill buffers, load ports are shared between threads on the same physical
>>> core.
>>> We need to run more than one vm on the same physical core.
>>> Is there any complete mitigation for environments utilizing SMT?
>> No - not really.
>>
>> An approach which was worked on was that of synchronised scheduling,
>> whereby privilege transitions are syncrhonised to ensure that we're
>> never running code from different privilege levels concurrently on
>> adjacent threads. (This is the mitigation described as Group Scheduling
>> in
>> https://software.intel.com/security-software-guidance/insights/deep-dive-intel-analysis-microarchitectural-data-sampling
>> )
> synchronised scheduling is not a complete mitigation. Guest A and Guest B
> run on the same physical core, and the privilege level is the same. So
> Guest A can infer data from Guest B. Guest A cannot infer data from hypervisor
> because they are in different privilege levels.
This is (one of the reasons) why core scheduling is a prerequisite to
synchronised scheduling.
With core scheduling active, you will never have guest A and B
concurrently running on adjacent threads of the same core.
~Andrew
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