linux-kernel - Re: [PATCH] Conform L3 Cache Index Disable to Linux standards

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Date:	Thu, 19 Feb 2009 02:24:30 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mark Langsdorf <mark.langsdorf@....com>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com
Subject: Re: [PATCH] Conform L3 Cache Index Disable to Linux standards

On Wed, 18 Feb 2009 16:04:26 -0600 Mark Langsdorf <mark.langsdorf@....com> wrote:

> The L3 Cache Index Disable feature to arch/x86/kernel/cpu/intel_cacheinfo.c
> accepted in 2.6.28 was inadvertently a preliminary version of the patch
> that should not have been accepted.  It did not include ABI documentation
> and did not meet the usage standards of a /sys file.
> 
> This patch changes that code to use a proposed patch that had the
> maintainer's approval but was accidentally not accepted.
> 
> It also corrects prevents the patch from being used on AMD processors
> that do not currently support L3 Cache Index Disable.
> 
> ...
>
> +show_cache_disable_##index(struct _cpuid4_info *this_leaf, char *buf)  	\
> +{									\
> +	return show_cache_disable(this_leaf, buf, index);		\
> +}
> +
> +static ssize_t
> +store_cache_disable(struct _cpuid4_info *this_leaf, const char *buf,
> +		 size_t count, unsigned int index)
> +{
> +	int node = cpu_to_node(first_cpu(this_leaf->shared_cpu_map));
> +	struct pci_dev *dev = k8_northbridges[node];
> +	ssize_t ret = 0;
> +	unsigned int val;
> +
> +	if (!this_leaf->can_disable)
> +		return -EINVAL;
> +
> +	ret = sscanf(buf, "%x", &val);

We permit used input suzh as `42foo'?

strict_strtoul() would fix that.

> +	if (ret != 1)
> +		return -EINVAL;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;

It would make sense to do this earlier in the function.

Do we need to do it at all?  File permissions do not suffice?

> +	val |= 0xc0000000;
> +	pci_write_config_dword(dev, 0x1BC + index * 4, val & ~0x40000000);
> +	wbinvd();
> +	pci_write_config_dword(dev, 0x1BC + index * 4, val);
> +	return count;
> +}
> +

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