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From: Borislav Petkov <bp@alien8.de>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Mario Gzuk <mariogzuk@technikz.de>
Subject: Re: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID
Date: Thu, 29 Nov 2012 10:13:17 +0100
Message-ID: <20121129091317.GA21084@liondog.tnic> (raw)
In-Reply-To: <50B6A8F3.5000407@zytor.com>

On Wed, Nov 28, 2012 at 04:14:43PM -0800, H. Peter Anvin wrote:
> Wrong barrier semantics.

Let me try to understand what you mean by that :)

Now, your version's asm output looks like this:

----
	.loc 2 95 0
	movl	$139, %esi	#, tmp140
	xorl	%eax, %eax	# tmp141
	movl	%esi, %ecx	# tmp140,
	movl	%eax, %edx	# tmp141,
#APP
# 95 "/home/boris/kernel/linux-2.6/arch/x86/include/asm/msr.h" 1
	wrmsr
# 0 "" 2
#NO_APP
	.loc 3 694 0
	movb	$1, %al	#,
#APP
# 694 "/home/boris/kernel/linux-2.6/arch/x86/include/asm/processor.h" 1
	cpuid
# 0 "" 2
.LVL15:
#NO_APP
----

This is the sync_core() call from early_init_intel(). Now look like 139
remains in %ecx after the WRMSR and CPUID actually gets called with
RAX=1 and RCX=139 (btw, 139 is MSR_IA32_UCODE_REV). Even if this works
I'd say, we don't want to have any stray values in RCX when doing CPUID,
no?

Now here's the version with the change I proposed:

----
	.loc 2 95 0
	xorl	%esi, %esi	# tmp144
	movl	$139, %edi	#, tmp143
	movl	%edi, %ecx	# tmp143,
	movl	%esi, %eax	# tmp144,
	movl	%esi, %edx	# tmp144,
#APP
# 95 "/home/boris/kernel/linux-2.6/arch/x86/include/asm/msr.h" 1
	wrmsr
# 0 "" 2
.LVL15:
#NO_APP
	.loc 3 199 0
	movb	$1, %al	#,
	movl	%esi, %ecx	# tmp144, ecx
#APP
# 199 "/home/boris/kernel/linux-2.6/arch/x86/include/asm/processor.h" 1
	cpuid
# 0 "" 2
.LVL16:
#NO_APP
----

RCX gets correctly cleaned to 0 and *then* we call CPUID.

And the asm output is the same except that RCX gets correctly cleaned up
before calling CPUID.

So what am I missing?

Thanks.

-- 
Regards/Gruss,
    Boris.

  reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-11-28 19:50 [PATCH 0/8] RFC: Remove 386 support H. Peter Anvin
2012-11-28 19:50 ` [PATCH 1/8] x86, 386 removal: Remove CONFIG_M386 from Kconfig H. Peter Anvin
2012-12-01  0:34   ` [tip:x86/nuke386] " tip-bot for H. Peter Anvin
2012-11-28 19:50 ` [PATCH 2/8] x86, 386 removal: Remove CONFIG_CMPXCHG H. Peter Anvin
2012-12-01  0:35   ` [tip:x86/nuke386] " tip-bot for H. Peter Anvin
2012-11-28 19:50 ` [PATCH 3/8] x86, 386 removal: Remove CONFIG_XADD H. Peter Anvin
2012-11-28 20:30   ` Borislav Petkov
2012-12-01  0:36   ` [tip:x86/nuke386] " tip-bot for H. Peter Anvin
2012-11-28 19:50 ` [PATCH 4/8] x86, 386 removal: Remove CONFIG_BSWAP H. Peter Anvin
2012-12-01  0:37   ` [tip:x86/nuke386] " tip-bot for H. Peter Anvin
2012-11-28 19:50 ` [PATCH 5/8] x86, 386 removal: Remove CONFIG_INVLPG H. Peter Anvin
2012-12-01  0:38   ` [tip:x86/nuke386] " tip-bot for H. Peter Anvin
2012-11-28 19:50 ` [PATCH 6/8] x86, 386 removal: Remove CONFIG_X86_WP_WORKS_OK H. Peter Anvin
2012-11-28 20:52   ` Alan Cox
2012-11-28 23:11     ` H. Peter Anvin
2012-12-01  0:42     ` [tip:x86/nuke386] x86, 386 removal: Document Nx586 as a 386 and thus unsupported tip-bot for H. Peter Anvin
2012-12-01  0:39   ` [tip:x86/nuke386] x86, 386 removal: Remove CONFIG_X86_WP_WORKS_OK tip-bot for H. Peter Anvin
2012-11-28 19:50 ` [PATCH 7/8] x86, 386 removal: Remove CONFIG_X86_POPAD_OK H. Peter Anvin
2012-12-01  0:40   ` [tip:x86/nuke386] " tip-bot for H. Peter Anvin
2012-11-28 19:50 ` [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID H. Peter Anvin
2012-11-28 20:41   ` Borislav Petkov
2012-11-29  0:14     ` H. Peter Anvin
2012-11-29  9:13       ` Borislav Petkov [this message]
2012-11-29 21:06         ` H. Peter Anvin
2012-11-29 21:18           ` Borislav Petkov
2012-11-29 21:20             ` H. Peter Anvin
2012-11-29 21:31               ` Borislav Petkov
2012-11-29 21:24     ` H. Peter Anvin
2012-11-29 21:34       ` Borislav Petkov
2012-11-30 17:01       ` Linus Torvalds
2012-11-30 17:28         ` Borislav Petkov
2012-11-30 18:03         ` H. Peter Anvin
2012-11-30 18:10           ` Borislav Petkov
2012-11-30 18:40             ` H. Peter Anvin
2012-12-01  0:41   ` [tip:x86/nuke386] " tip-bot for H. Peter Anvin

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