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Date:   Fri, 16 Jun 2023 01:39:22 -0700
From:   Breno Leitao <leitao@debian.org>
To:     Andi Kleen <ak@linux.intel.com>
Cc:     pawan.kumar.gupta@linux.intel.com, jpoimboe@kernel.org,
        peterz@infradead.org, tglx@linutronix.de, bp@alien8.de,
        leit@fb.com, hpa@zytor.com, x86@kernel.org, mingo@redhat.com,
        dave.hansen@linux.intel.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] x86/bugs: Break down mitigations configurations
Message-ID: <ZIwfuvaRFNqZyCC7@gmail.com>
References: <20230615164417.3588162-1-leitao@debian.org>
 <87352shc98.fsf@linux.intel.com>
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On Thu, Jun 15, 2023 at 10:21:55AM -0700, Andi Kleen wrote:
> Breno Leitao <leitao@debian.org> writes:
> 
> > There is no way to compile a kernel today with some of the speculative
> > mitigations disabled. Even if the kernel has
> > CONFIG_SPECULATION_MITIGATIONS=n, some Intel mitigations, such as MDS, TAA,
> > MMIO are still enabled and can only be disabled using a kernel parameter.
> >
> > This patchset creates a way to choose what to enable or disable, and,
> > get the mitigations disable if CONFIG_SPECULATION_MITIGATIONS is not
> > set, as the rest of other mitigations.
> >
> > Also, we want to print a warning message letting users know that these
> > mitigations are disabled.
> >
> > This is a follow up to this discussion: https://lkml.org/lkml/2023/6/12/798
> >
> 
> Isn't this all roughly equivalent to CONFIG_CMDLINE="mitigations=..." ?

It is, indeed. But, the main motivation for this patchset it to solve a
consistency problem on our Kconfig. The user would image that all
speculative mitigations would be disabled if he passes
CONFIG_SPECULATION_MITIGATIONS=n, but that is not true. The user needs
something else, such as CONFIG_CMDLINE="mitigations=off" or "mds=off".

This patchset give more consistency to our Kconfig options, and the user
doesn't need to read between the lines.