linux-kernel - Re: [patch 1/2] sysfs/cpu: Add vulnerability folder

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Message-ID: <20180107211951.GA26115@kroah.com>
Date:   Sun, 7 Jan 2018 22:19:51 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "Hansen, Dave" <dave.hansen@...el.com>
Subject: Re: [patch 1/2] sysfs/cpu: Add vulnerability folder

On Sun, Jan 07, 2018 at 09:57:50PM +0100, Thomas Gleixner wrote:
> As the meltdown/spectre problem affects several CPU architectures, it makes
> sense to have common way to express whether a system is affected by a
> particular vulnerability or not. If affected the way to express the
> mitigation should be common as well.
> 
> Create /sys/devices/system/cpu/vulnerabilities folder and files for
> meltdown, spectre_v1 and spectre_v2.

I like this, minor nits below:

> 
> Allow architextures to override the show function.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  drivers/base/Kconfig |    3 +++
>  drivers/base/cpu.c   |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/cpu.h  |    7 +++++++
>  3 files changed, 58 insertions(+)

A Documentation/ABI/ update is needed for the new sysfs files.

> +#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES
> +
> +ssize_t __weak cpu_show_meltdown(struct device *dev,
> +				 struct device_attribute *attr, char *buf)
> +{
> +	return snprintf(buf, PAGE_SIZE - 2, "Not affected\n");

sysfs is one-value-per-file, so you never need to care about the page
size, a simple sprintf() is fine.  No need to change if you don't want
to, your call.

> +}
> +
> +ssize_t __weak cpu_show_spectre_v1(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	return snprintf(buf, PAGE_SIZE - 2, "Not affected\n");
> +}
> +
> +ssize_t __weak cpu_show_spectre_v2(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	return snprintf(buf, PAGE_SIZE - 2, "Not affected\n");
> +}
> +
> +static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
> +static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
> +static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);

DEVICE_ATTR_RO() please.

Yeah, that does make the global symbols a bit different, meltdown_show()
and the like.  Hm, I guess this is ok, given that it's ment to be
overridden.

Oh, nevermind.  So, just a documentation update please, that can always
be an add-on patch if you promise to do it :)

thanks,

greg k-h