linux-kernel - Re: [RFC][PATCH v2 00/21] x86/pti: Defer CR3 switch to C code

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Date:   Wed, 18 Nov 2020 08:08:48 +0100
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org,
        thomas.lendacky@....com, jroedel@...e.de, konrad.wilk@...cle.com,
        jan.setjeeilers@...cle.com, junaids@...gle.com, oweisse@...gle.com,
        rppt@...ux.vnet.ibm.com, graf@...zon.de, mgross@...ux.intel.com,
        kuzuno@...il.com
Subject: Re: [RFC][PATCH v2 00/21] x86/pti: Defer CR3 switch to C code


On 11/17/20 10:23 PM, Borislav Petkov wrote:
> On Tue, Nov 17, 2020 at 08:02:51PM +0100, Alexandre Chartre wrote:
>> No. This prevents the guest VM from gathering data from the host
>> kernel on the same cpu-thread. But there's no mitigation for a guest
>> VM running on a cpu-thread attacking another cpu-thread (which can be
>> running another guest VM or the host kernel) from the same cpu-core.
>> You cannot use flush/clear barriers because the two cpu-threads are
>> running in parallel.
> 
> Now there's your justification for why you're doing this. It took a
> while...
> 
> The "why" should always be part of the 0th message to provide
> reviewers/maintainers with answers to the question, what this pile of
> patches is all about. Please always add this rationale to your patchset
> in the future.
> 

Sorry about that, I will definitively try to do better next time. :-}

Thanks,

alex.