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Subject[PATCH x86 for review III] [25/29] i386: paravirt unhandled fallthrough
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From: Rusty Russell <rusty@rustcorp.com.au>
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@rustcorp.com.au>
Signed-off-by: Andi Kleen <ak@suse.de>

---
arch/i386/kernel/Makefile | 2 --
arch/i386/kernel/head.S | 7 ++++++-
arch/i386/kernel/paravirt.c | 3 ---
3 files changed, 6 insertions(+), 6 deletions(-)

Index: linux/arch/i386/kernel/Makefile
===================================================================
--- linux.orig/arch/i386/kernel/Makefile
+++ linux/arch/i386/kernel/Makefile
@@ -41,8 +41,6 @@ obj-$(CONFIG_HPET_TIMER) += hpet.o
obj-$(CONFIG_K8_NB) += k8.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
Index: linux/arch/i386/kernel/head.S
===================================================================
--- linux.orig/arch/i386/kernel/head.S
+++ linux/arch/i386/kernel/head.S
@@ -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 @@ startup_paravirt:

addl $4, (%esp)
jmp 1b
+
+unhandled_paravirt:
+ /* Nothing wanted us: we're screwed. */
+ ud2
#endif

/*
Index: linux/arch/i386/kernel/paravirt.c
===================================================================
--- linux.orig/arch/i386/kernel/paravirt.c
+++ linux/arch/i386/kernel/paravirt.c
@@ -482,9 +482,6 @@ static int __init print_banner(void)
}
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",
.paravirt_enabled = 0,
-
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