linux-kernel - Re: [tip:x86/urgent] x86/boot: Initialize FPU and X86_FEATURE

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Message-ID: <20160930151538.GA14423@nazgul.tnic>
Date:   Fri, 30 Sep 2016 17:15:38 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     linux-tip-commits@...r.kernel.org, david@...giorato.net,
        brgerst@...il.com, peterz@...radead.org, dave@...1.net,
        dvlasenk@...hat.com, mingo@...nel.org, jpoimboe@...hat.com,
        hpa@...or.com, luto@...nel.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: [tip:x86/urgent] x86/boot: Initialize FPU and X86_FEATURE_ALWAYS
 even if we don't have CPUID

On Fri, Sep 30, 2016 at 05:06:46AM -0700, tip-bot for Andy Lutomirski wrote:
> Commit-ID:  05fb3c199bb09f5b85de56cc3ede194ac95c5e1f
> Gitweb:     http://git.kernel.org/tip/05fb3c199bb09f5b85de56cc3ede194ac95c5e1f
> Author:     Andy Lutomirski <luto@...nel.org>
> AuthorDate: Wed, 28 Sep 2016 16:06:33 -0700
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Fri, 30 Sep 2016 13:53:04 +0200
> 
> x86/boot: Initialize FPU and X86_FEATURE_ALWAYS even if we don't have CPUID
> 
> Otherwise arch_task_struct_size == 0 and we die.  While we're at it,
> set X86_FEATURE_ALWAYS, too.

...

> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 809eda0..bcc9ccc 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()) {

Let's make it even simpler:

---
From: Borislav Petkov <bp@...e.de>
Date: Fri, 30 Sep 2016 17:08:10 +0200
Subject: [PATCH] x86/boot: Streamline CPUID check conditional

We have now:

	if (!have_cpuid_p())
		...

	if (have_cpuid_p())
		...

Turn it into a good, ole if-else conditional which is much more
readable.

No functionality change.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/common.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 9bd910a7dd0a..0a6fa6174ed8 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -800,9 +800,6 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 	memset(&c->x86_capability, 0, sizeof c->x86_capability);
 	c->extended_cpuid_level = 0;
 
-	if (!have_cpuid_p())
-		identify_cpu_without_cpuid(c);
-
 	/* cyrix could have cpuid enabled via c_identify()*/
 	if (have_cpuid_p()) {
 		cpu_detect(c);
@@ -817,6 +814,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 
 		if (this_cpu->c_bsp_init)
 			this_cpu->c_bsp_init(c);
+	} else {
+		identify_cpu_without_cpuid(c);
 	}
 
 	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
-- 
2.8.4

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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