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Date:   Tue, 17 Nov 2020 22:23:07 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Alexandre Chartre <alexandre.chartre@oracle.com>
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
Subject: Re: [RFC][PATCH v2 00/21] x86/pti: Defer CR3 switch to C code
Message-ID: <20201117212307.GR5719@zn.tnic>
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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.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette