[PATCH 11/15] x86: disable virtualization on all CPUs if needed, on emergency_restart

Eduardo Habkost
2008-11-05T19:56:54Z

On emergency_restart, we may need to use an NMI to disable virtualization
on all CPUs. We do that by using nmi_shootdown_cpus(), but only if a
virt_disable function was set by KVM.

Finding a proper point to hook the nmi_shootdown_cpus() call isn't
trivial, as the non-emergency machine_restart() (that doesn't need the
NMI tricks) uses machine_emergency_restart() directly.

The solution to make this work without adding a new function or argument
to machine_ops was setting a 'reboot_emergency' flag that tells if
native_machine_emergency_restart() needs to do the virt cleanup or not.

[v2: additional source code comments explaining why we do that]

Signed-off-by: Eduardo Habkost <ehabkost-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
arch/x86/kernel/reboot.c | 55 ++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 407106e..3240491 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -12,6 +12,7 @@
#include <asm/proto.h>
#include <asm/reboot_fixups.h>
#include <asm/reboot.h>
+#include <asm/virtext.h>

#ifdef CONFIG_X86_32
# include <linux/dmi.h>
@@ -42,6 +43,12 @@ int reboot_force;
static int reboot_cpu = -1;
#endif

+/* This is set if we need to go through the 'emergency' path.
+ * When machine_emergency_restart() is called, we may be on
+ * an inconsistent state and won't be able to do a clean cleanup
+ */
+static int reboot_emergency;
+
/* reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old]
warm Don't set the cold reboot flag
cold Set the cold reboot flag
@@ -357,6 +364,40 @@ static inline void kb_wait(void)
}
}

+static void disable_virt_nmi(int cpu, struct die_args *args)
+{
+ emergency_virt_disable();
+}
+
+/* Use NMIs as IPIs to tell all CPUs to disable virtualization
+ */
+static void emergency_virt_disable_all(void)
+{
+ /* We need to disable virtualization extensions on all CPUs
+ * before rebooting, otherwise we risk hanging up the machine,
+ * because the CPU ignore INIT signals when VMX is enabled.
+ *
+ * We can't take any locks and we may be on an inconsistent
+ * state, so we use NMIs as IPIs to tell the other CPUs to halt.
+ *
+ * For safety, we will try to do this only when we may have
+ * virtualization enabled.
+ */
+ if (has_virt_extensions()) {
+ /* Kill the other CPUs */
+ nmi_shootdown_cpus(disable_virt_nmi);
+ /* Disable virt on this CPU */
+ emergency_virt_disable();
+ }
+
+ /* If another CPU call set_virt_disable_func()
+ * here, we will be lost. Unless we want to add the NMI
+ * stuff to the reboot path for non-virt users, we will
+ * have to live with this (unlikely) possibility.
+ */
+
+}
+
void __attribute__((weak)) mach_reboot_fixups(void)
{
}
@@ -365,9 +406,13 @@ static void native_machine_emergency_restart(void)
{
int i;

+ if (reboot_emergency)
+ emergency_virt_disable_all();
+
/* Tell the BIOS if we want cold or warm reboot */
*((unsigned short *)__va(0x472)) = reboot_mode;

+
for (;;) {
/* Could also try the reset bit in the Hammer NB */
switch (reboot_type) {
@@ -456,13 +501,19 @@ void native_machine_shutdown(void)
#endif
}

+static void __machine_emergency_restart(int emergency)
+{
+ reboot_emergency = emergency;
+ machine_ops.emergency_restart();
+}
+
static void native_machine_restart(char *__unused)
{
printk("machine restart\n");

if (!reboot_force)
machine_shutdown();
- machine_emergency_restart();
+ __machine_emergency_restart(0);
}

static void native_machine_halt(void)
@@ -501,7 +552,7 @@ void machine_shutdown(void)

void machine_emergency_restart(void)
{
- machine_ops.emergency_restart();
+ __machine_emergency_restart(1);
}

void machine_restart(char *cmd)
--
1.5.5.GIT