From ed72736183c45a413a8d6974dd04be90f514cb6b Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 30 Dec 2020 16:26:55 -0800 Subject: [PATCH] x86/reboot: Force all cpus to exit VMX root if VMX is supported Force all CPUs to do VMXOFF (via NMI shootdown) during an emergency reboot if VMX is _supported_, as VMX being off on the current CPU does not prevent other CPUs from being in VMX root (post-VMXON). This fixes a bug where a crash/panic reboot could leave other CPUs in VMX root and prevent them from being woken via INIT-SIPI-SIPI in the new kernel. Fixes: d176720d34c7 ("x86: disable VMX on all CPUs on reboot") Cc: stable@vger.kernel.org Suggested-by: Sean Christopherson Signed-off-by: David P. Reed [sean: reworked changelog and further tweaked comment] Signed-off-by: Sean Christopherson Message-Id: <20201231002702.2223707-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kernel/reboot.c | 30 ++++++++++-------------------- 1 file changed, 10 insertions(+), 20 deletions(-) diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c index db115943e8bd..efbaef8b4de9 100644 --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -538,31 +538,21 @@ static void emergency_vmx_disable_all(void) local_irq_disable(); /* - * We need to disable VMX on all CPUs before rebooting, otherwise - * we risk hanging up the machine, because the CPU ignores INIT - * signals when VMX is enabled. + * Disable VMX on all CPUs before rebooting, otherwise we risk hanging + * the machine, because the CPU blocks INIT when it's in VMX root. * - * 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 disable - * VMX and halt. + * We can't take any locks and we may be on an inconsistent state, so + * use NMIs as IPIs to tell the other CPUs to exit VMX root and halt. * - * For safety, we will avoid running the nmi_shootdown_cpus() - * stuff unnecessarily, but we don't have a way to check - * if other CPUs have VMX enabled. So we will call it only if the - * CPU we are running on has VMX enabled. - * - * We will miss cases where VMX is not enabled on all CPUs. This - * shouldn't do much harm because KVM always enable VMX on all - * CPUs anyway. But we can miss it on the small window where KVM - * is still enabling VMX. + * Do the NMI shootdown even if VMX if off on _this_ CPU, as that + * doesn't prevent a different CPU from being in VMX root operation. */ - if (cpu_has_vmx() && cpu_vmx_enabled()) { - /* Disable VMX on this CPU. */ - cpu_vmxoff(); + if (cpu_has_vmx()) { + /* Safely force _this_ CPU out of VMX root operation. */ + __cpu_emergency_vmxoff(); - /* Halt and disable VMX on the other CPUs */ + /* Halt and exit VMX root operation on the other CPUs. */ nmi_shootdown_cpus(vmxoff_nmi); - } } -- 2.11.0