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

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Date: Fri, 26 Apr 2024 10:08:57 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Chao Gao <chao.gao@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...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, 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!