linux-kernel - Re: [PATCH 4.9 13/20] x86/speculation/mmio: Add mitigation for Processor MMIO Stale Data

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Date:   Wed, 22 Jun 2022 13:48:44 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rdunlap@...radead.org
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Subject: Re: [PATCH 4.9 13/20] x86/speculation/mmio: Add mitigation for
 Processor MMIO Stale Data

Hi!


> +static int __init mmio_stale_data_parse_cmdline(char *str)
> +{
> +	if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))
> +		return 0;
> +
> +	if (!str)
> +		return -EINVAL;
> +
> +	if (!strcmp(str, "off")) {
> +		mmio_mitigation = MMIO_MITIGATION_OFF;
> +	} else if (!strcmp(str, "full")) {
> +		mmio_mitigation = MMIO_MITIGATION_VERW;
> +	} else if (!strcmp(str, "full,nosmt")) {
> +		mmio_mitigation = MMIO_MITIGATION_VERW;
> +		mmio_nosmt = true;
> +	}
> +
> +	return 0;
> +}

This is wrong, AFAICT. Returning 0 will pollute init's environment;
Randy was cleaning those lately and we are even seeing them in
-stable. See for example b793a01000122d2bd133ba451a76cc135b5e162c.

The early return 0 should disappear, too; we should validate the
option even on non-buggy machines.

Best regards,
								Pavel

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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