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

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Message-ID: <20201117212307.GR5719@zn.tnic>
Date:   Tue, 17 Nov 2020 22:23:07 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Alexandre Chartre <alexandre.chartre@...cle.com>
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 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