From 7f798d67af24a7a28768537d932eecc56dd0435b Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@redhat.com>
Date: Sun, 5 Dec 2010 14:23:53 -0200
Subject: [PATCH 1/2] KVM: Don't spin on virt instruction faults during reboot

RH-Author: Avi Kivity <avi@redhat.com>
Message-id: <1291559034-31793-2-git-send-email-avi@redhat.com>
Patchwork-id: 14225
O-Subject: [PATCH RHEL5.5.z 1/2] KVM: Don't spin on virt instruction faults
	during reboot
Bugzilla: 661397
RH-Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
RH-Acked-by: Gleb Natapov <gleb@redhat.com>
RH-Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>

Bugzilla: 608709
Upstream: kvm.git 94acad998c

Since vmx blocks INIT signals, we disable virtualization extensions during
reboot.  This leads to virtualization instructions faulting; we trap these
faults and spin while the reboot continues.

Unfortunately spinning on a non-preemptible kernel may block a task that
reboot depends on; this causes the reboot to hang.

Fix by skipping over the instruction and hoping for the best.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |    8 ++++++--
 virt/kvm/kvm_main.c             |   11 ++++-------
 2 files changed, 10 insertions(+), 9 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |    8 ++++++--
 virt/kvm/kvm_main.c             |   11 ++++-------
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b9dff51..e60478d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -737,14 +737,18 @@ enum {
  * reboot turns off virtualization while processes are running.
  * Trap the fault and ignore the instruction if that happens.
  */
-asmlinkage void kvm_handle_fault_on_reboot(void);
+asmlinkage void kvm_spurious_fault(void);
+extern bool kvm_rebooting;
 
 #define __kvm_handle_fault_on_reboot(insn) \
 	"666: " insn "\n\t" \
+	"668: \n\t"                           \
 	".pushsection .fixup, \"ax\" \n" \
 	"667: \n\t" \
+	"cmpb $0, kvm_rebooting \n\t"	      \
+	"jne 668b \n\t"      		      \
 	__ASM_SIZE(push) " $666b \n\t"	      \
-	"jmp kvm_handle_fault_on_reboot \n\t" \
+	"call kvm_spurious_fault \n\t"	      \
 	".popsection \n\t" \
 	".pushsection __ex_table, \"a\" \n\t" \
 	_ASM_PTR " 666b, 667b \n\t" \
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index de582db..950fe04 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -77,7 +77,8 @@ struct dentry *kvm_debugfs_dir;
 static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl,
 			   unsigned long arg);
 
-static bool kvm_rebooting;
+bool kvm_rebooting;
+EXPORT_SYMBOL_GPL(kvm_rebooting);
 
 #ifdef KVM_CAP_DEVICE_ASSIGNMENT
 static struct kvm_assigned_dev_kernel *kvm_find_assigned_dev(struct list_head *head,
@@ -2403,16 +2404,12 @@ static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
 }
 
 
-asmlinkage void kvm_handle_fault_on_reboot(void)
+asmlinkage void kvm_spurious_fault(void)
 {
-	if (kvm_rebooting)
-		/* spin while reset goes on */
-		while (true)
-			;
 	/* Fault while not rebooting.  We want the trace. */
 	BUG();
 }
-EXPORT_SYMBOL_GPL(kvm_handle_fault_on_reboot);
+EXPORT_SYMBOL_GPL(kvm_spurious_fault);
 
 static int kvm_reboot(struct notifier_block *notifier, unsigned long val,
 		      void *v)
-- 
1.7.3.2