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Subject: Re: [RFC v2 00/27] Kernel Address Space Isolation
To:     Peter Zijlstra <peterz@infradead.org>
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        rppt@linux.vnet.ibm.com, Paul Turner <pjt@google.com>
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From:   Alexandre Chartre <alexandre.chartre@oracle.com>
Organization: Oracle Corporation
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Date:   Fri, 12 Jul 2019 14:47:23 +0200
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On 7/12/19 2:36 PM, Peter Zijlstra wrote:
> On Fri, Jul 12, 2019 at 02:17:20PM +0200, Alexandre Chartre wrote:
>> On 7/12/19 1:44 PM, Peter Zijlstra wrote:
> 
>>> AFAIK3 this wants/needs to be combined with core-scheduling to be
>>> useful, but not a single mention of that is anywhere.
>>
>> No. This is actually an alternative to core-scheduling. Eventually, ASI
>> will kick all sibling hyperthreads when exiting isolation and it needs to
>> run with the full kernel page-table (note that's currently not in these
>> patches).
>>
>> So ASI can be seen as an optimization to disabling hyperthreading: instead
>> of just disabling hyperthreading you run with ASI, and when ASI can't preserve
>> isolation you will basically run with a single thread.
> 
> You can't do that without much of the scheduler changes present in the
> core-scheduling patches.
> 

We hope we can do that without the whole core-scheduling mechanism. The idea
is to send an IPI to all sibling hyperthreads. This IPI will interrupt these
sibling hyperthreads and have them wait for a condition that will allow them
to resume execution (for example when re-entering isolation). We are
investigating this in parallel to ASI.

alex.