Re: [PATCH v3 3/6] KVM: nVMX: Load nEPT state after EFER

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2013-09-02 15:16, Gleb Natapov wrote:
> On Thu, Aug 08, 2013 at 04:26:30PM +0200, Jan Kiszka wrote:
>> We need to update EFER.NX before building the nEPT state via
>> nested_ept_init_mmu_context. Otherwise, we risk to create an MMU context
>> that claims to have NX disabled while the guest EPT used NX. This will
>> cause spurious faults for L2.
>>
> Hmm, I do not see how nested ept mmu depends on guests EFER.NX setting.
> It just sets mmu->nx to true.

Don't ask me for the details behind this, but update_permission_bitmask
called by kvm_init_shadow_ept_mmu is using it e.g. And the
"before-after" effect was clearly visible when L2 and L1 were using
different NX settings. Maybe Arthur can write a test for this.

Jan

> 
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>  arch/x86/kvm/vmx.c |   10 +++++-----
>>  1 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 6c42518..363fe19 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -7727,11 +7727,6 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>>  		vmx_flush_tlb(vcpu);
>>  	}
>>  
>> -	if (nested_cpu_has_ept(vmcs12)) {
>> -		kvm_mmu_unload(vcpu);
>> -		nested_ept_init_mmu_context(vcpu);
>> -	}
>> -
>>  	if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_EFER)
>>  		vcpu->arch.efer = vmcs12->guest_ia32_efer;
>>  	else if (vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE)
>> @@ -7741,6 +7736,11 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>>  	/* Note: modifies VM_ENTRY/EXIT_CONTROLS and GUEST/HOST_IA32_EFER */
>>  	vmx_set_efer(vcpu, vcpu->arch.efer);
>>  
>> +	if (nested_cpu_has_ept(vmcs12)) {
>> +		kvm_mmu_unload(vcpu);
>> +		nested_ept_init_mmu_context(vcpu);
>> +	}
>> +
>>  	/*
>>  	 * This sets GUEST_CR0 to vmcs12->guest_cr0, with possibly a modified
>>  	 * TS bit (for lazy fpu) and bits which we consider mandatory enabled.
>> -- 
>> 1.7.3.4
> 
> --
> 			Gleb.
> 

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