From 59765db5fc82726b32876b794667e2c6936a98ab Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 21 Jul 2023 13:18:47 -0700 Subject: [PATCH] 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: Kai Huang Link: https://lore.kernel.org/r/20230721201859.2307736-8-seanjc@google.com Signed-off-by: Sean Christopherson --- 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 85cb2df..98e5db3 100644 --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -22,7 +22,6 @@ #include #include #include -#include #include #include #include @@ -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(); -- 2.7.4