Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 12 Jun 2023 06:46:16 -0700
From:   Breno Leitao <leitao@debian.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        pawan.kumar.gupta@linux.intel.com, paul@paul-moore.com,
        leit@meta.com, x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cpu/bugs: Disable CPU mitigations at compilation time
Message-ID: <ZIchqLWousxkCqyB@gmail.com>
References: <20230203120615.1121272-1-leitao@debian.org>
 <87352z7xld.ffs@tglx>
 <ZIcVoIAQbRl1GTo5@gmail.com>
 <20230612133230.GJZIcebkHxd8QJs0Dv@fat_crate.local>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230612133230.GJZIcebkHxd8QJs0Dv@fat_crate.local>
Precedence: bulk

On Mon, Jun 12, 2023 at 03:32:30PM +0200, Borislav Petkov wrote:
> On Mon, Jun 12, 2023 at 05:54:56AM -0700, Breno Leitao wrote:
> > 1) We keep consistency with other CONFIG options. Linux already has a
> > CONFIG option to enable/disable mitigations for speculations
> > (CONFIG_SPECULATION_MITIGATIONS), so, this will be a similar one.
> 
> So you can get what you want by disabling all those options there,
> right?

This patch proposes creating CONFIG_CPU_MITIGATIONS_DEFAULT_OFF that
will turn all the mitigations off in a binary, which is the same as
passing mitigations=off in the command line when the kernel boots.

Setting CONFIG_SPECULATION_MITIGATIONS=n does *not* disable all the
mitigations, as, there are some mitigations that are *not* disabled when
you pass CONFIG_SPECULATION_MITIGATIONS=n. As an example (from my
memory - need to double check in 6.4), MDS and TAA mitigations are not
disabled when CONFIG_SPECULATION_MITIGATIONS=n. MDS and TAA mitigations
are disabled when `mitigations=off` parameter is passed, tho.