linux-kernel - Re: [PATCH v3 17/18] KVM: x86: Force kvm_rebooting=true during emergency reboot/crash

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Message-ID: <73ea9a6075898081871b0a164a5779900f2e54b5.camel@intel.com>
Date:   Tue, 23 May 2023 02:02:37 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Gao, Chao" <chao.gao@...el.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v3 17/18] KVM: x86: Force kvm_rebooting=true during
 emergency reboot/crash

On Tue, 2023-05-23 at 11:25 +1200, Kai Huang wrote:
> On Fri, 2023-05-12 at 16:50 -0700, Sean Christopherson wrote:
> > Set kvm_rebooting when virtualization is disabled in an emergency so that
> > KVM eats faults on virtualization instructions even if kvm_reboot() isn't
> > reached.
> > 
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >  arch/x86/kvm/svm/svm.c | 2 ++
> >  arch/x86/kvm/vmx/vmx.c | 2 ++
> >  2 files changed, 4 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index 2cc195d95d32..d00da133b14f 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -611,6 +611,8 @@ static inline void kvm_cpu_svm_disable(void)
> >  
> >  static void svm_emergency_disable(void)
> >  {
> > +	kvm_rebooting = true;
> > +
> >  	kvm_cpu_svm_disable();
> >  }
> >  
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 008914396180..1dec932aff21 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -771,6 +771,8 @@ static void vmx_emergency_disable(void)
> >  	int cpu = raw_smp_processor_id();
> >  	struct loaded_vmcs *v;
> >  
> > +	kvm_rebooting = true;
> 
> Do we need a memory barrier here?
> 

Hmm.. Please ignore this.  I was confused between cache coherency vs memory
ordering.  Not enough coffee.

Reviewed-by: Kai Huang <kai.huang@...el.com>