linux-kernel - Re: [RFC PATCH] x86/boot: Initialize FPU and X86_FEATURE

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Date:   Fri, 30 Sep 2016 10:32:45 +0200
From:   David Saggiorato <david@...giorato.net>
To:     Andy Lutomirski <luto@...nel.org>, x86@...nel.org
Cc:     Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Dave Hansen <dave@...1.net>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH] x86/boot: Initialize FPU and X86_FEATURE_ALWAYS
 even if we don't have CPUID

Tested-by: David Saggiorato <david@...giorato.net>Le mercredi 28 septembre 2016 à 16:06 -0700, Andy Lutomirski a écrit :
> Otherwise arch_task_struct_size == 0 and we die.  While we're at it,
> set X86_FEATURE_ALWAYS, too.
> 
> Cc: stable@...r.kernel.org
> Cc: Dave Hansen <dave@...1.net>
> Cc: Ingo Molnar <mingo@...nel.org>
> Fixes: aaeb5c01c5b ("x86/fpu, sched: Introduce
> CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT and use it on x86")
> Reported-by: david@...giorato.net
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
> 
> Totally untested except by the 0-day bot, since I don't have an
> affected machine and QEMU can't emulate anything without CPUID.
> 
>  arch/x86/kernel/cpu/common.c | 23 +++++++++++------------
>  1 file changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c
> b/arch/x86/kernel/cpu/common.c
> index 809eda03c527..bcc9ccc220c9 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -804,21 +804,20 @@ static void __init early_identify_cpu(struct
> cpuinfo_x86 *c)
>  		identify_cpu_without_cpuid(c);
>  
>  	/* cyrix could have cpuid enabled via c_identify()*/
> -	if (!have_cpuid_p())
> -		return;
> +	if (have_cpuid_p()) {
> +		cpu_detect(c);
> +		get_cpu_vendor(c);
> +		get_cpu_cap(c);
>  
> -	cpu_detect(c);
> -	get_cpu_vendor(c);
> -	get_cpu_cap(c);
> -
> -	if (this_cpu->c_early_init)
> -		this_cpu->c_early_init(c);
> +		if (this_cpu->c_early_init)
> +			this_cpu->c_early_init(c);
>  
> -	c->cpu_index = 0;
> -	filter_cpuid_features(c, false);
> +		c->cpu_index = 0;
> +		filter_cpuid_features(c, false);
>  
> -	if (this_cpu->c_bsp_init)
> -		this_cpu->c_bsp_init(c);
> +		if (this_cpu->c_bsp_init)
> +			this_cpu->c_bsp_init(c);
> +	}
>  
>  	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
>  	fpu__init_system(c);
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