KVM: Don't spin on virt instruction faults during reboot

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>

2 files changed, 10 insertions, 11 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 56e45a2ed2de..d968cc501799 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -786,14 +786,18 @@ 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 ee99b77e4451..7f686251f711 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -90,7 +90,8 @@ static void hardware_disable_all(void);
 
 static void kvm_io_bus_destroy(struct kvm_io_bus *bus);
 
-static bool kvm_rebooting;
+bool kvm_rebooting;
+EXPORT_SYMBOL_GPL(kvm_rebooting);
 
 static bool largepages_enabled = true;
 
@@ -2171,18 +2172,12 @@ 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 */
-                local_irq_enable();
-                while (true)
-                        cpu_relax();
-        }
         /* 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)