Re: [PATCH v3 5/6] KVM: nVMX: Update mmu.base_role.nxe after EFER loading on VM-entry/exit

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

On 2013-09-03 11:04, Gleb Natapov wrote:
> On Tue, Sep 03, 2013 at 10:51:31AM +0200, Jan Kiszka wrote:
>> On 2013-09-03 10:39, Gleb Natapov wrote:
>>> On Thu, Aug 08, 2013 at 04:26:32PM +0200, Jan Kiszka wrote:
>>>> This job is normally performed by the architectural EFER set service
>>>> which we cannot use as it prevents transitions that are valid when
>>>> switching between L1 and L2. So open-code the update of base_role.nxe
>>>> after changing EFER on VM-entry and exit.
>>>>
>>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>>> ---
>>>>  arch/x86/kvm/vmx.c |    4 ++++
>>>>  1 files changed, 4 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>> index 9b0510b..7cc208a 100644
>>>> --- a/arch/x86/kvm/vmx.c
>>>> +++ b/arch/x86/kvm/vmx.c
>>>> @@ -7735,6 +7735,8 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>>>>  		vcpu->arch.efer &= ~(EFER_LMA | EFER_LME);
>>>>  	/* Note: modifies VM_ENTRY/EXIT_CONTROLS and GUEST/HOST_IA32_EFER */
>>>>  	vmx_set_efer(vcpu, vcpu->arch.efer);
>>>> +	vcpu->arch.mmu.base_role.nxe =
>>>> +		(vcpu->arch.efer & EFER_NX) && !enable_ept;
>>>>  
>>> kvm_mmu_reset_context() called later in this function does that.
>>
>> For all relevant scenarios? The code is pretty convoluted, so this is
>> non-obvious for me: kvm_mmu_reset_context calls init_kvm_mmu which may
>> call init_kvm_softmmu that does kvm_init_shadow_mmu with nxe
>> initialization. But is that path always taken?
>>
> What scenarios are relevant here? kvm_mmu_reset_context() is what
> kvm_set_efer() would have called anyway. Since you use !enable_ept
> here I assume that relevant scenario is shadow on shadow and in this
> case it is easy to see that kvm_mmu_reset_context() will call
> kvm_init_shadow_mmu() eventually. For all other scenarios guest nx
> setting is irrelevant.

Indeed... Ah! I missed that 2c9afa52 changed the picture. OK, another
obsolete one.

Jan

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