Re: [PATCH] x86: do not allow to optimize flag_is_changeable_p()(rev. 2)

[Ingo Molnar]

* Krzysztof Helt <krzysztof.h1@xxxxx> wrote:

> From: Krzysztof Helt <krzysztof.h1@xxxxx>
> 
> The flag_is_changeable_p() is used by
> has_cpuid_p() which can return different results
> in the code sequence below:
> 
>  if (!have_cpuid_p())
>       identify_cpu_without_cpuid(c);
> 
>   /* cyrix could have cpuid enabled via c_identify()*/
>   if (!have_cpuid_p())
>       return;
> 
> Otherwise, the gcc 3.4.6 optimizes these two calls
> into one which make the code not working correctly.
> 
> Cyrix cpus have the CPUID instruction enabled before
> the second call to the have_cpuid_p() but
> it is not detected due to the gcc optimization.
> Thus the ARR registers (mtrr like) are not detected
> on such a cpu.
> 
> Signed-off-by: Krzysztof Helt <krzysztof.h1@xxxxx>

applied to tip/x86/core, thanks Krzysztof!

	Ingo
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