linux-kernel - [PATCH 1/7] cleanup: paravirt unhandled fallthrough

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Date:	Mon, 12 Feb 2007 14:32:00 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.osdl.org>,
	Andi Kleen <ak@....de>
Subject: [PATCH 1/7] cleanup: paravirt unhandled fallthrough

The current code simply calls "start_kernel" directly if we're under a
hypervisor and no paravirt_ops backend wants us, because paravirt.c
registers that as a backend.

This was always a vain hope; start_kernel won't get far without setup.
It's also impossible for paravirt_ops backends which don't sit in the
arch/i386/kernel directory: they can't link before paravirt.o anyway.

Keep it simple: if we pass all the registered paravirt probes, BUG().

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

diff -r 4fb7fc327801 arch/i386/kernel/Makefile
--- a/arch/i386/kernel/Makefile	Mon Feb 12 12:37:01 2007 +1100
+++ b/arch/i386/kernel/Makefile	Mon Feb 12 12:55:00 2007 +1100
@@ -41,8 +41,6 @@ obj-$(CONFIG_KWATCH)		+= debugreg.o kwat
 obj-$(CONFIG_KWATCH)		+= debugreg.o kwatch.o
 
 obj-$(CONFIG_VMI)		+= vmi.o vmitime.o
-
-# Make sure this is linked after any other paravirt_ops structs: see head.S
 obj-$(CONFIG_PARAVIRT)		+= paravirt.o
 
 EXTRA_AFLAGS   := -traditional
diff -r 4fb7fc327801 arch/i386/kernel/head.S
--- a/arch/i386/kernel/head.S	Mon Feb 12 12:37:01 2007 +1100
+++ b/arch/i386/kernel/head.S	Mon Feb 12 12:54:19 2007 +1100
@@ -513,10 +513,11 @@ startup_paravirt:
 	pushl	%ecx
 	pushl	%eax
 
-	/* paravirt.o is last in link, and that probe fn never returns */
 	pushl	$__start_paravirtprobe
 1:
 	movl	0(%esp), %eax
+	cmpl	$__stop_paravirtprobe, %eax
+	je	unhandled_paravirt
 	pushl	(%eax)
 	movl	8(%esp), %eax
 	call	*(%esp)
@@ -528,6 +529,10 @@ 1:
 
 	addl	$4, (%esp)
 	jmp	1b
+
+unhandled_paravirt:
+	/* Nothing wanted us: we're screwed. */ 
+	ud2
 #endif
 
 /*
diff -r 4fb7fc327801 arch/i386/kernel/paravirt.c
--- a/arch/i386/kernel/paravirt.c	Mon Feb 12 12:37:01 2007 +1100
+++ b/arch/i386/kernel/paravirt.c	Mon Feb 12 12:54:19 2007 +1100
@@ -481,9 +481,6 @@ static int __init print_banner(void)
 	return 0;
 }
 core_initcall(print_banner);
-
-/* We simply declare start_kernel to be the paravirt probe of last resort. */
-paravirt_probe(start_kernel);
 
 struct paravirt_ops paravirt_ops = {
 	.name = "bare hardware",


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