Messages in this thread Patch in this message | | | From | Vitaly Kuznetsov <> | Subject | Re: [PATCH 2/2] x86/reboot: Disable virtualization in an emergency if SVM is supported | Date | Thu, 12 May 2022 10:37:44 +0200 |
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Sean Christopherson <seanjc@google.com> writes:
> Disable SVM on all CPUs via NMI shootdown during an emergency reboot. > Like VMX, SVM can block INIT and thus prevent bringing up other CPUs via > INIT-SIPI-SIPI. > > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kernel/reboot.c | 26 ++++++++++++++------------ > 1 file changed, 14 insertions(+), 12 deletions(-) > > diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c > index f9543a4e9b09..33c1f4883b27 100644 > --- a/arch/x86/kernel/reboot.c > +++ b/arch/x86/kernel/reboot.c > @@ -533,27 +533,29 @@ static void nmi_shootdown_nop(int cpu, struct pt_regs *regs) > /* Nothing to do, the NMI shootdown handler disables virtualization. */ > } > > -/* Use NMIs as IPIs to tell all CPUs to disable virtualization */ > -static void emergency_vmx_disable_all(void) > +static void emergency_reboot_disable_virtualization(void) > { > /* Just make sure we won't change CPUs while doing this */ > local_irq_disable(); > > /* > - * Disable VMX on all CPUs before rebooting, otherwise we risk hanging > - * the machine, because the CPU blocks INIT when it's in VMX root. > + * Disable virtualization on all CPUs before rebooting to avoid hanging > + * the system, as VMX and SVM block INIT when running in the host > * > * 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. > + * use NMIs as IPIs to tell the other CPUs to disable VMX/SVM and halt. > * > - * 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. > + * Do the NMI shootdown even if virtualization is off on _this_ CPU, as > + * other CPUs may have virtualization enabled. > */ > - if (cpu_has_vmx()) { > - /* Safely force _this_ CPU out of VMX root operation. */ > - __cpu_emergency_vmxoff(); > + if (cpu_has_vmx() || cpu_has_svm(NULL)) { > + /* Safely force _this_ CPU out of VMX/SVM operation. */ > + if (cpu_has_vmx()) > + __cpu_emergency_vmxoff(); > + else > + cpu_emergency_svm_disable(); > > - /* Halt and exit VMX root operation on the other CPUs. */ > + /* Disable VMX/SVM and halt on other CPUs. */ > nmi_shootdown_cpus(nmi_shootdown_nop); > }
Nitpicking: we can get rid of the second cpu_has_vmx() if we write this as:
if (cpu_has_vmx()) __cpu_emergency_vmxoff(); else if (cpu_has_svm(NULL)) cpu_emergency_svm_disable(); else return;
nmi_shootdown_cpus(nmi_shootdown_nop);
> } > @@ -590,7 +592,7 @@ static void native_machine_emergency_restart(void) > unsigned short mode; > > if (reboot_emergency) > - emergency_vmx_disable_all(); > + emergency_reboot_disable_virtualization(); > > tboot_shutdown(TB_SHUTDOWN_REBOOT);
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
-- Vitaly
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