Commit 59765db5 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

x86/reboot: Disable virtualization during reboot iff callback is registered 



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).

Checking for a valid callback instead of simply for SVM or VMX support
can also eliminates spurious NMIs by avoiding the unecessary call to
nmi_shootdown_cpus_on_restart().

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

Reviewed-by: default avatarKai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230721201859.2307736-8-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent edc8deb0

arch/x86/kernel/reboot.c

+1 −2
Original line number Diff line number Diff line
@@ -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>
@@ -589,7 +588,7 @@ 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. */

		cpu_emergency_disable_virtualization();