This is a note to let you know that I've just added the patch titled x86/reboot: Force all cpus to exit VMX root if VMX is supported to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-reboot-force-all-cpus-to-exit-vmx-root-if-vmx-is-supported.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From ed72736183c45a413a8d6974dd04be90f514cb6b Mon Sep 17 00:00:00 2001 From: Sean Christopherson <seanjc@xxxxxxxxxx> Date: Wed, 30 Dec 2020 16:26:55 -0800 Subject: x86/reboot: Force all cpus to exit VMX root if VMX is supported From: Sean Christopherson <seanjc@xxxxxxxxxx> commit ed72736183c45a413a8d6974dd04be90f514cb6b upstream. 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@xxxxxxxxxxxxxxx Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> Signed-off-by: David P. Reed <dpreed@xxxxxxxxxxxx> [sean: reworked changelog and further tweaked comment] Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Message-Id: <20201231002702.2223707-3-seanjc@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/reboot.c | 29 ++++++++++------------------- 1 file changed, 10 insertions(+), 19 deletions(-) --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -538,29 +538,20 @@ static void emergency_vmx_disable_all(vo local_irq_disable(); /* - * We need to disable VMX on all CPUs before rebooting, otherwise - * we risk hanging up the machine, because the CPU ignore 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); } Patches currently in stable-queue which might be from seanjc@xxxxxxxxxx are queue-4.19/x86-reboot-force-all-cpus-to-exit-vmx-root-if-vmx-is-supported.patch