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Subject: Re: [RFC v2 00/27] Kernel Address Space Isolation
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     pbonzini@redhat.com, rkrcmar@redhat.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        dave.hansen@linux.intel.com, luto@kernel.org, kvm@vger.kernel.org,
        x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        konrad.wilk@oracle.com, jan.setjeeilers@oracle.com,
        liran.alon@oracle.com, jwadams@google.com, graf@amazon.de,
        rppt@linux.vnet.ibm.com, Paul Turner <pjt@google.com>
References: <1562855138-19507-1-git-send-email-alexandre.chartre@oracle.com>
 <20190712114458.GU3402@hirez.programming.kicks-ass.net>
From:   Alexandre Chartre <alexandre.chartre@oracle.com>
Organization: Oracle Corporation
Message-ID: <1f97f1d9-d209-f2ab-406d-fac765006f91@oracle.com>
Date:   Fri, 12 Jul 2019 14:17:20 +0200
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On 7/12/19 1:44 PM, Peter Zijlstra wrote:
> On Thu, Jul 11, 2019 at 04:25:12PM +0200, Alexandre Chartre wrote:
>> Kernel Address Space Isolation aims to use address spaces to isolate some
>> parts of the kernel (for example KVM) to prevent leaking sensitive data
>> between hyper-threads under speculative execution attacks. You can refer
>> to the first version of this RFC for more context:
>>
>>     https://lkml.org/lkml/2019/5/13/515
> 
> No, no, no!
> 
> That is the crux of this entire series; you're not punting on explaining
> exactly why we want to go dig through 26 patches of gunk.
> 
> You get to exactly explain what (your definition of) sensitive data is,
> and which speculative scenarios and how this approach mitigates them.
> 
> And included in that is a high level overview of the whole thing.
> 

Ok, I will rework the explanation. Sorry about that.

> On the one hand you've made this implementation for KVM, while on the
> other hand you're saying it is generic but then fail to describe any
> !KVM user.
> 
> AFAIK all speculative fails this is relevant to are now public, so
> excruciating horrible details are fine and required.

Ok.

> AFAIK2 this is all because of MDS but it also helps with v1.

Yes, mostly MDS and also L1TF.

> 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.

I will add all that to the explanation.

Thanks,

alex.