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	<1283011478-27237-3-git-send-email-brgerst@gmail.com>
Date: Sun, 29 Aug 2010 21:29:40 +0300
Message-ID: <AANLkTinReUPW4auBZCHVZcHfZfMxEOa1qmaY+npV=UPY@mail.gmail.com>
Subject: Re: [PATCH 02/11] x86: Merge fpu_init()
From: Pekka Enberg <penberg@kernel.org>
To: Brian Gerst <brgerst@gmail.com>
Cc: hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org
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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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