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

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Message-ID: <AANLkTin6pZq_JquweSMrWfZsCM79v=1TqUConNa85rFN@mail.gmail.com>
Date:	Sun, 29 Aug 2010 20:44:06 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] x86: Merge fpu_init()

On Sun, Aug 29, 2010 at 2:29 PM, Pekka Enberg <penberg@...nel.org> wrote:
> 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().
>

Good catch, will fix.
--
Brian Gerst
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