Re: [PATCH 1/3] x86: Bugfix bit-rot in the calling of legacy_cache_size

[Thomas Gleixner <tglx@linutronix.de>]

On Tue, 30 Sep 2014, Bryan O'Donoghue wrote:
>  static void default_init(struct cpuinfo_x86 *c)
>  {
> -#ifdef CONFIG_X86_64
>  	cpu_detect_cache_sizes(c);
> -#else
> +
>  	/* Not much we can do here... */
>  	/* Check if at least it has cpuid */
>  	if (c->cpuid_level == -1) {
> @@ -79,7 +78,6 @@ static void default_init(struct cpuinfo_x86 *c)
>  		else if (c->x86 == 3)
>  			strcpy(c->x86_model_id, "386");
>  	}
> -#endif

What's the exact point of this? This is the default init function
which is for X86_VENDOR_UNKNOWN, right?

>  }
>  
>  static const struct cpu_dev default_cpu = {
> @@ -874,6 +872,15 @@ static void identify_cpu(struct cpuinfo_x86 *c)
>  #endif
>  
>  	/*
> +	 * If c_x86_vendor != X86_VENDOR_UNKNOWN i.e. a known vendor then
> +	 * there's a vendor specific c_init()
> +	 *
> +	 * Even still Intel, AMD and VIA make use of legacy_cache_size which
> +	 * is reachable only through default_init right now

That's nonsense. It's called from cpu_detect_cache_sizes() and that is
called from:

arch/x86/kernel/cpu/amd.c:      cpu_detect_cache_sizes(c);
arch/x86/kernel/cpu/centaur.c:  cpu_detect_cache_sizes(c);
arch/x86/kernel/cpu/common.c:   cpu_detect_cache_sizes(c);
arch/x86/kernel/cpu/cyrix.c:            cpu_detect_cache_sizes(c);
arch/x86/kernel/cpu/transmeta.c:        cpu_detect_cache_sizes(c);

So we have 4 callsites outside of default_init() already. Now you're
adding another one into identify_cpu()

> +	 */
> +	if (this_cpu->c_x86_vendor != X86_VENDOR_UNKNOWN)
> +		default_init(c);

With the consequence that for amd/centaur/cyrix/transmeta
cpu_detect_cache_sizes() is invoked twice for nothing.

So the only CPU vendor c_init() callback which does not call
cpu_detect_cache_sizes() is the Intel one. And therefor we inflict
that call on all others twice. Brilliant solution!

So the proper solution is to add the call to identify_cpu()
unconditionally and remove it from _all_ other call sites, make it
static and be done with it.

Sigh,

	tglx