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    SubjectRe: [PATCH 02/11] x86: Merge fpu_init()
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    On Sat, Aug 28, 2010 at 7:04 PM, Brian Gerst <brgerst@gmail.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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