linux-kernel - Re: [PATCH 02/11] x86: Merge fpu

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Message-ID: <AANLkTinReUPW4auBZCHVZcHfZfMxEOa1qmaY+npV=UPY@mail.gmail.com>
Date:	Sun, 29 Aug 2010 21:29:40 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Brian Gerst <brgerst@...il.com>
Cc:	hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] x86: Merge fpu_init()

On Sat, Aug 28, 2010 at 7:04 PM, Brian Gerst <brgerst@...il.com> wrote:
> @@ -80,7 +80,6 @@ static void __cpuinit init_thread_xstate(void)
>  #endif
>  }
>
> -#ifdef CONFIG_X86_64
>  /*
>  * Called at bootup to set up the initial FPU state that is later cloned
>  * into all processes.
> @@ -88,12 +87,20 @@ static void __cpuinit init_thread_xstate(void)
>
>  void __cpuinit fpu_init(void)
>  {
> -       unsigned long oldcr0 = read_cr0();
> +       unsigned long cr0;
> +       unsigned long cr4_mask = 0;
>
> -       set_in_cr4(X86_CR4_OSFXSR);
> -       set_in_cr4(X86_CR4_OSXMMEXCPT);
> +       if (cpu_has_fxsr)
> +               cr4_mask |= X86_CR4_OSFXSR;
> +       if (cpu_has_xmm)
> +               cr4_mask |= X86_CR4_OSXMMEXCPT;
> +       set_in_cr4(cr4_mask);

Is calling set_in_cr4() unconditionally safe for 32-bit CPUs that
don't have cr4? AFAICT, no, because it uses read_cr4().
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