[PATCH v3 05/18] x86/reboot: Disable virtualization during reboot iff callback is registered

From: Sean Christopherson
Date: Fri May 12 2023 - 19:50:59 EST

Attempt to disable virtualization during an emergency reboot if and only
if there is a registered virt callback, i.e. iff a hypervisor (KVM) is
active. If there's no active hypervisor, then the CPU can't be operating
with VMX or SVM enabled (barring an egregious bug).

Note, IRQs are disabled, which prevents KVM from coming along and enabling
virtualization after the fact.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
arch/x86/kernel/reboot.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 92b380e199a3..20f7bdabc52e 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -22,7 +22,6 @@
#include <asm/reboot_fixups.h>
#include <asm/reboot.h>
#include <asm/pci_x86.h>
-#include <asm/virtext.h>
#include <asm/cpu.h>
#include <asm/nmi.h>
#include <asm/smp.h>
@@ -545,7 +544,7 @@ static void emergency_reboot_disable_virtualization(void)
* Do the NMI shootdown even if virtualization is off on _this_ CPU, as
* other CPUs may have virtualization enabled.
- if (cpu_has_vmx() || cpu_has_svm(NULL)) {
+ if (rcu_access_pointer(cpu_emergency_virt_callback)) {
/* Safely force _this_ CPU out of VMX/SVM operation. */