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From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Mon, 15 Apr 2024 13:13:36 +0200
Message-ID: <CAMuHMdVjB2g+fN8dxcmHUjKhzDChPpwcf8hMCbf=arOK5MkOuQ@mail.gmail.com>
Subject: Re: [PATCH 1/3] x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n
To: Sean Christopherson <seanjc@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, 
	Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, 
	Peter Zijlstra <peterz@infradead.org>, Josh Poimboeuf <jpoimboe@kernel.org>, linux-doc@vger.kernel.org, 
	linux-kernel@vger.kernel.org, Pawan Gupta <pawan.kumar.gupta@linux.intel.com>, 
	Daniel Sneddon <daniel.sneddon@linux.intel.com>, Catalin Marinas <catalin.marinas@arm.com>, 
	Will Deacon <will@kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, 
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>
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Hi Sean,

On Tue, Apr 9, 2024 at 7:51=E2=80=AFPM Sean Christopherson <seanjc@google.c=
om> wrote:
> Initialize cpu_mitigations to CPU_MITIGATIONS_OFF if the kernel is built
> with CONFIG_SPECULATION_MITIGATIONS=3Dn, as the help text quite clearly
> states that disabling SPECULATION_MITIGATIONS is supposed to turn off all
> mitigations by default.
>
>   =E2=94=82 If you say N, all mitigations will be disabled. You really
>   =E2=94=82 should know what you are doing to say so.
>
> As is, the kernel still defaults to CPU_MITIGATIONS_AUTO, which results i=
n
> some mitigations being enabled in spite of SPECULATION_MITIGATIONS=3Dn.
>
> Fixes: f43b9876e857 ("x86/retbleed: Add fine grained Kconfig knobs")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Thanks for your patch, which is now commit f337a6a21e2fd67e
("x86/cpu: Actually turn off mitigations by default
for SPECULATION_MITIGATIONS=3Dn") in v6.9-rc4.

This causes the following suspicious messages on R-Car H3:

        CPU features: kernel page table isolation forced OFF by mitigations=
=3Doff
        spectre-v4 mitigation disabled by command-line option
        spectre-v2 mitigation disabled by command line option
        spectre-v2 mitigation disabled by command line option

and R-Car V4H:

        CPU features: kernel page table isolation forced OFF by mitigations=
=3Doff
        spectre-v4 mitigation disabled by command-line option
        spectre-bhb mitigation disabled by command line option
        spectre-bhb mitigation disabled by command line option

Interestingly, no mitigations are disabled on the command-line.

Gr{oetje,eeting}s,

                        Geert

--=20
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds