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Subject: Re: [RFC][PATCH v2 00/21] x86/pti: Defer CR3 switch to C code
To:     Borislav Petkov <bp@alien8.de>
Cc:     tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
        x86@kernel.org, dave.hansen@linux.intel.com, luto@kernel.org,
        peterz@infradead.org, linux-kernel@vger.kernel.org,
        thomas.lendacky@amd.com, jroedel@suse.de, konrad.wilk@oracle.com,
        jan.setjeeilers@oracle.com, junaids@google.com, oweisse@google.com,
        rppt@linux.vnet.ibm.com, graf@amazon.de, mgross@linux.intel.com,
        kuzuno@gmail.com
References: <20201116144757.1920077-1-alexandre.chartre@oracle.com>
 <20201116201711.GE1131@zn.tnic>
 <44a88648-738a-4a4b-9c25-6b70000e037c@oracle.com>
 <20201117165539.GG5719@zn.tnic>
 <890f6b7e-a268-2257-edcb-5eacc7db3d8e@oracle.com>
 <20201117182809.GK5719@zn.tnic>
 <33a1c6ee-0122-0b0c-ed2d-1578b29ef7c1@oracle.com>
 <20201117212307.GR5719@zn.tnic>
From:   Alexandre Chartre <alexandre.chartre@oracle.com>
Message-ID: <1c39ebd0-2afd-5f51-ef48-ea3f378d8a0d@oracle.com>
Date:   Wed, 18 Nov 2020 08:08:48 +0100
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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.