linux-kernel - Re: [PATCH 2/4] KVM: x86: Register emergency virt callback in common code, via kvm_x86

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Message-ID: <cb59d42e0ce59c6e6f3e9af019654687b04c4f5d.camel@intel.com>
Date: Mon, 13 May 2024 12:55:02 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>, "Gao, Chao" <chao.gao@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] KVM: x86: Register emergency virt callback in common
 code, via kvm_x86_ops

On Fri, 2024-04-26 at 10:08 -0700, Sean Christopherson wrote:
> On Fri, Apr 26, 2024, Chao Gao wrote:
> > > diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> > > index 502704596c83..afddfe3747dd 100644
> > > --- a/arch/x86/kvm/vmx/x86_ops.h
> > > +++ b/arch/x86/kvm/vmx/x86_ops.h
> > > @@ -15,6 +15,7 @@ void vmx_hardware_unsetup(void);
> > > int vmx_check_processor_compat(void);
> > > int vmx_hardware_enable(void);
> > > void vmx_hardware_disable(void);
> > > +void vmx_emergency_disable(void);
> > > int vmx_vm_init(struct kvm *kvm);
> > > void vmx_vm_destroy(struct kvm *kvm);
> > > int vmx_vcpu_precreate(struct kvm *kvm);
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index e9ef1fa4b90b..12e88aa2cca2 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -9797,6 +9797,8 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
> > > 
> > > 	kvm_ops_update(ops);
> > > 
> > > +	cpu_emergency_register_virt_callback(kvm_x86_ops.emergency_disable);
> > > +
> > 
> > vmx_emergency_disable() accesses loaded_vmcss_on_cpu but now it may be called
> > before loaded_vmcss_on_cpu is initialized. This may be not a problem for now
> > given the check for X86_CR4_VMXE  in vmx_emergency_disable(). But relying on
> > that check is fragile. I think it is better to apply the patch below from Isaku
> > before this patch.
> > 
> > https://lore.kernel.org/kvm/c1b7f0e5c2476f9f565acda5c1e746b8d181499b.1708933498.git.isaku.yamahata@intel.com/
> 
> Agreed, good eyeballs, and thanks for the reviews!
> 

I think we can even move registering this emergency disable to
hardware_enable_all()?  It seems there's no reason to register the
callback if hardware_enable_all() hasn't been attempted.