Messages in this thread | | | From | Andy Lutomirski <> | Date | Sun, 5 Jul 2020 11:26:03 -0700 | Subject | Re: [PATCH v3 3/3] Force all cpus to exit VMX root operation on crash/panic reliably |
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On Sat, Jul 4, 2020 at 1:38 PM David P. Reed <dpreed@deepplum.com> wrote: > > Fix the logic during crash/panic reboot on Intel processors that > can support VMX operation to ensure that all processors are not > in VMX root operation. Prior code made optimistic assumptions > about other cpus that would leave other cpus in VMX root operation > depending on timing of crash/panic reboot. > Builds on cpu_ermergency_vmxoff() and __cpu_emergency_vmxoff() created > in a prior patch. > > Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com> > Signed-off-by: David P. Reed <dpreed@deepplum.com> > --- > arch/x86/kernel/reboot.c | 20 +++++++------------- > 1 file changed, 7 insertions(+), 13 deletions(-) > > diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c > index 0ec7ced727fe..c8e96ba78efc 100644 > --- a/arch/x86/kernel/reboot.c > +++ b/arch/x86/kernel/reboot.c > @@ -543,24 +543,18 @@ static void emergency_vmx_disable_all(void) > * signals when VMX is enabled. > * > * 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. > + * state, so we use NMIs as IPIs to tell the other CPUs to exit > + * VMX root operation 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. > + * if other CPUs might be in VMX root operation. > */ > - if (cpu_has_vmx() && cpu_vmx_enabled()) { > - /* Disable VMX on this CPU. */ > - cpu_vmxoff(); > + if (cpu_has_vmx()) { > + /* Safely force out of VMX root operation on this CPU. */ > + __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); > > }
Seems reasonable to me.
As a minor caveat, doing cr4_clear_bits() in NMI context is not really okay, but we're about to reboot, so nothing too awful should happen. And this has very little to do with your patch.
Reviewed-by: Andy Lutomirski <luto@kernel.org>
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