linux-kernel - Re: [113/197] x86, cacheinfo: Calculate L3 indices

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Message-ID: <20100506141358.GB20994@aftab>
Date:	Thu, 6 May 2010 16:13:58 +0200
From:	Borislav Petkov <borislav.petkov@....com>
To:	Jiri Kosina <jkosina@...e.cz>
CC:	Greg KH <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...nel.org" <stable@...nel.org>,
	"stable-review@...nel.org" <stable-review@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Renninger <trenn@...e.de>, Jiri Benc <jbenc@...e.cz>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>,
	"Ostrovsky, Boris" <Boris.Ostrovsky@....com>
Subject: Re: [113/197] x86, cacheinfo: Calculate L3 indices

From: Jiri Kosina <jkosina@...e.cz>
Date: Thu, May 06, 2010 at 09:46:21AM -0400

> Well, we have
> 
> 	#ifdef CONFIG_K8_NB
> 	static inline struct pci_dev *node_to_k8_nb_misc(int node)
> 	{
> 		return (node < num_k8_northbridges) ? k8_northbridges[node] : NULL;
> 	}
> 	#else
> 	static inline struct pci_dev *node_to_k8_nb_misc(int node)
> 	{
> 		return NULL;
> 	}
> 	#endif
> 
> So it legitimately returns NULL in two cases:
> 
> 	1) if someone passes too large node
> 	2) if CONFIG_K8_NB is unset
> 
> 1) Either we assume that node will always be in the range (i.e. 
> amd_get_nb_id() will never go crazy return anything bogus), and then we 
> could just drop the test completely. Or we want to check for such the 
> possibility, and then node_to_k8_nb_misc() is going to return NULL in such 
> cases, and so we want to check for it.

No, we want to check it since K8_NB has many users - not only L3.

> 2) is now moot, as all three in-tree callers are now under proper ifdefs 
> (CONFIG_CPU_SUP_AMD, which depends on CONFIG_K8_NB after your patch has 
> been applied). So I believe we could remove it, right?

I don't think I understand "remove it" here. Which "it" you're referring to?

> Either way, current state seems inconsistent. So either we should add the 
> return value check to amd_calc_l3_indices() as well, or remove all the 
> NULL magic altogether, i.e. the (untested) patch below.
> 
> What do you think?

Take a look at 

http://git.kernel.org/?p=linux/kernel/git/x86/linux-2.6-tip.git;a=commitdiff;h=f2b20e41407fccfcfacf927ff91ec888832a37af

This does

+       if (num_k8_northbridges == 0)
+               return;

in amd_check_l3_disable().

So if K8_NB has failed initializing for some reason, we never go near
the pci devs and the node_to_k8_nb_misc() calls since we effectively
disable the L3 functionality.

Thus the NULL pointer checks you remove in the patch below are
superfluous, I agree, and I have already removed those in my tree along
with the other improvements/fixes I'm working on right now.

> 
> 
> From: Jiri Kosina <jkosina@...e.cz>
> Subject: x86, cacheinfo: remove unnecessary NULL pointer checks
> 
> As K8_NB thing is now always initialized on AMD CPUs, and we don't have 
> any caller that would be outside CONFIG_CPU_SUP_AMD/CONFIG_K8_NB, it is 
> safe to assume that kb_northbridges has been always initialized).
> 
> Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> 
>  arch/x86/include/asm/k8.h             |   10 +---------
>  arch/x86/kernel/cpu/intel_cacheinfo.c |    6 ------
>  2 files changed, 1 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/k8.h b/arch/x86/include/asm/k8.h
> index f70e600..0cff8ba 100644
> --- a/arch/x86/include/asm/k8.h
> +++ b/arch/x86/include/asm/k8.h
> @@ -15,17 +15,9 @@ extern int k8_get_nodes(struct bootnode *nodes);
>  extern int k8_numa_init(unsigned long start_pfn, unsigned long end_pfn);
>  extern int k8_scan_nodes(void);
>  
> -#ifdef CONFIG_K8_NB
>  static inline struct pci_dev *node_to_k8_nb_misc(int node)
>  {
> -	return (node < num_k8_northbridges) ? k8_northbridges[node] : NULL;
> +	return k8_northbridges[node];
>  }
> -#else
> -static inline struct pci_dev *node_to_k8_nb_misc(int node)
> -{
> -	return NULL;
> -}
> -#endif
> -
>  
>  #endif /* _ASM_X86_K8_H */
> diff --git a/arch/x86/kernel/cpu/intel_cacheinfo.c b/arch/x86/kernel/cpu/intel_cacheinfo.c
> index b3eeb66..6c5f3cd 100644
> --- a/arch/x86/kernel/cpu/intel_cacheinfo.c
> +++ b/arch/x86/kernel/cpu/intel_cacheinfo.c
> @@ -355,9 +355,6 @@ static ssize_t show_cache_disable(struct _cpuid4_info *this_leaf, char *buf,
>  	if (!this_leaf->can_disable)
>  		return -EINVAL;
>  
> -	if (!dev)
> -		return -EINVAL;
> -
>  	pci_read_config_dword(dev, 0x1BC + index * 4, &reg);
>  	return sprintf(buf, "0x%08x\n", reg);
>  }
> @@ -388,9 +385,6 @@ static ssize_t store_cache_disable(struct _cpuid4_info *this_leaf,
>  	if (!capable(CAP_SYS_ADMIN))
>  		return -EPERM;
>  
> -	if (!dev)
> -		return -EINVAL;
> -
>  	if (strict_strtoul(buf, 10, &val) < 0)
>  		return -EINVAL;
>  
> 
> -- 
> Jiri Kosina
> SUSE Labs, Novell Inc.
> 

-- 
Regards/Gruss,
Boris.

--
Advanced Micro Devices, Inc.
Operating Systems Research Center

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