From: Breno Leitao <leitao@debian.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.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
Date: Mon, 12 Jun 2023 05:54:56 -0700 [thread overview]
Message-ID: <ZIcVoIAQbRl1GTo5@gmail.com> (raw)
In-Reply-To: <87352z7xld.ffs@tglx>
On Sun, Jun 11, 2023 at 12:37:34AM +0200, Thomas Gleixner wrote:
> On Fri, Feb 03 2023 at 04:06, Breno Leitao wrote:
> > Right now it is not possible to disable CPU vulnerabilities mitigations
> > at build time. Mitigation needs to be disabled passing kernel
> > parameters, such as 'mitigations=off'.
> >
> > Create a new config option (CONFIG_CPU_MITIGATIONS_DEFAULT_OFF) that
> > sets the global variable `cpu_mitigations` to OFF, instead of AUTO. This
> > allows the creation of kernel binaries that boots with the CPU
> > mitigations turned off by default, and does not require dealing kernel
> > parameters.
>
> Why? What's the justification
There are two major justification from my point of view:
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.
2) There are companies that have different kernel flavours (different
CONFIG options basically), for different type of workloads, and a
machine can change their kernel flavors a few times a day. I.e, for
a specifically workload, boots in flavor X since it works the best.
Mitigation enabled/disabled is key to some of these flavors.
I would like to see a flavor as self-contained in a binary that I can
mix and match. Right not they are not, since for some kernel
flavours, you need to add kernel command lines (mitigations=off), which
requires some hard logic, mainly when you are dealing with kexec and
grub.
next prev parent reply other threads:[~2023-06-12 12:56 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-03 12:06 [PATCH] cpu/bugs: Disable CPU mitigations at compilation time Breno Leitao
2023-06-09 17:33 ` Borislav Petkov
2023-06-12 11:22 ` David Laight
2023-06-12 11:51 ` Borislav Petkov
2023-06-12 12:16 ` David Laight
2023-06-12 13:27 ` Borislav Petkov
2023-06-10 22:37 ` Thomas Gleixner
2023-06-12 12:54 ` Breno Leitao [this message]
2023-06-12 13:32 ` Borislav Petkov
2023-06-12 13:46 ` Breno Leitao
2023-06-12 13:53 ` Borislav Petkov
2023-06-12 14:16 ` Breno Leitao
2023-06-12 16:08 ` Borislav Petkov
2023-06-12 16:37 ` Breno Leitao
2023-06-12 17:05 ` Borislav Petkov
2023-06-13 16:02 ` Breno Leitao
2023-06-13 16:20 ` Borislav Petkov
2023-06-12 17:26 ` Thomas Gleixner
2023-06-12 18:06 ` Randy Dunlap
2023-06-12 18:13 ` Borislav Petkov
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