diff mbox series

[v4,07/19] x86/reboot: Disable virtualization during reboot iff callback is registered

Message ID 20230721201859.2307736-8-seanjc@google.com
State New
Headers
Series x86/reboot: KVM: Clean up "emergency" virt code |

Commit Message

Sean Christopherson July 21, 2023, 8:18 p.m. UTC 
  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.

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

Comments

Kai Huang July 24, 2023, 11:57 p.m. UTC | #1 
On Fri, 2023-07-21 at 13:18 -0700, Sean Christopherson wrote:
> 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.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> 

Reviewed-by: Kai Huang <kai.huang@intel.com>
diff mbox series

Patch

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 85cb2dfcb67b..98e5db3fd7f4 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>
@@ -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();