Message-ID: <16e3217b-1561-51ea-7514-014e27240402@intel.com>
Date:   Tue, 31 Jan 2023 14:48:05 -0800
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Subject: Re: [PATCH] x86: enable Data Operand Independent Timing Mode
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To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Jann Horn <jannh@google.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H . Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-hardening@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Roxana Bradescu <roxabee@chromium.org>,
        Adam Langley <agl@google.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        "Jason A . Donenfeld" <Jason@zx2c4.com>
References: <20230125012801.362496-1-ebiggers@kernel.org>
 <14506678-918f-81e1-2c26-2b347ff50701@intel.com>
 <CAG48ez1NaWarARJj5SBdKKTYFO2MbX7xO75Rk0Q2iK8LX4BwFA@mail.gmail.com>
 <394c92e2-a9aa-37e1-7a34-d7569ac844fd@intel.com>
 <CAG48ez0ZK3pMqkto4DTZPNyddYcv8jPHQDNhYoFEPvSRLf80fQ@mail.gmail.com>
 <e37a17c4-8611-6d1d-85ad-fcd04ff285e1@intel.com> <Y9MAvhQYlOe4l2BM@gmail.com>
 <8b2771ce-9cfa-54cc-de6b-e80ce7af0a93@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <8b2771ce-9cfa-54cc-de6b-e80ce7af0a93@intel.com>
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We've been talking about this inside Intel.  Suffice to say that DOITM
was not designed to be turned on all the time.  If software turns it on
all the time, it won't accomplish what it was designed to do.

The _most_ likely thing that's going to happen is that DOITM gets
redefined to be much more limited in scope.  The current DOITM
architecture is very broad, but the implementations have much more
limited effects.  This means that the architecture can probably be
constrained and still match the hardware that's out there today.  That's
pure speculation (ha!) on my part.

I think we should hold off on merging any DOITM patches until the dust
settles.  As far as I know, there is no pressing practical reason to
apply something urgently.

Any objections?