Linux Virtualization - Apr 2007 - [PATCH 0/10] lguest

This patch series is against 2.6.20; some things are in flux, so there
might be issues as other things flow into the latest -git tree.
>From the documentation:
Lguest is designed to be a minimal hypervisor for the Linux kernel, for
Linux developers and users to experiment with virtualization with the
minimum of complexity.  Nonetheless, it should have sufficient
features to make it useful for specific tasks, and, of course, you are
encouraged to fork and enhance it.

Features:

- Kernel module which runs in a normal kernel.
- Simple I/O model for communication.
- Simple program to create new guests.
- Logo contains cute puppies: http://lguest.ozlabs.org

Developer features:

- Fun to hack on.
- No ABI: being tied to a specific kernel anyway, you can change
anything.
- Many opportunities for improvement or feature implementation.

Cheers!
Rusty

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 and it's linked last.

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.

This implements a real fallthrough if we pass all the registered
paravirt probes.

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

==================================================================---
a/arch/i386/kernel/Makefile
+++ b/arch/i386/kernel/Makefile
@@ -39,8 +39,6 @@ obj-$(CONFIG_EARLY_PRINTK)	+= early_prin
 obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
 obj-$(CONFIG_HPET_TIMER) 	+= hpet.o
 obj-$(CONFIG_K8_NB)		+= k8.o
-
-# Make sure this is linked after any other paravirt_ops structs: see head.S
 obj-$(CONFIG_PARAVIRT)		+= paravirt.o
 
 EXTRA_AFLAGS   := -traditional
==================================================================---
a/arch/i386/kernel/head.S
+++ b/arch/i386/kernel/head.S
@@ -502,10 +502,11 @@ 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)
@@ -517,6 +518,12 @@ 1:
 
 	addl	$4, (%esp)
 	jmp	1b
+
+unhandled_paravirt:
+	/* Nothing wanted us: try to die with dignity (impossible trap). */ 
+	movl	$0x1F, %edx
+	pushl	$0
+	jmp	early_fault
 #endif
 
 /*
==================================================================---
a/arch/i386/kernel/paravirt.c
+++ b/arch/i386/kernel/paravirt.c
@@ -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",