Re: [PATCH v3 01/13] nEPT: Support LOAD_IA32_EFER entry/exit controls for L1

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-07-02 15:59, Gleb Natapov wrote:
> On Tue, Jul 02, 2013 at 03:01:24AM +0000, Zhang, Yang Z wrote:
>> Since this series is pending in mail list for long time. And it's really a big feature for Nested. Also, I doubt the original authors(Jun and Nahav)should not have enough time to continue it. So I will pick it up. :)
>>
>> See comments below:
>>
>> Paolo Bonzini wrote on 2013-05-20:
>>> Il 19/05/2013 06:52, Jun Nakajima ha scritto:
>>>> From: Nadav Har'El <nyh@il.ibm.com>
>>>>
>>>> Recent KVM, since
>>> http://kerneltrap.org/mailarchive/linux-kvm/2010/5/2/6261577
>>>> switch the EFER MSR when EPT is used and the host and guest have different
>>>> NX bits. So if we add support for nested EPT (L1 guest using EPT to run L2)
>>>> and want to be able to run recent KVM as L1, we need to allow L1 to use this
>>>> EFER switching feature.
>>>>
>>>> To do this EFER switching, KVM uses VM_ENTRY/EXIT_LOAD_IA32_EFER if
>>> available,
>>>> and if it isn't, it uses the generic VM_ENTRY/EXIT_MSR_LOAD. This patch adds
>>>> support for the former (the latter is still unsupported).
>>>>
>>>> Nested entry and exit emulation (prepare_vmcs_02 and
>>> load_vmcs12_host_state,
>>>> respectively) already handled VM_ENTRY/EXIT_LOAD_IA32_EFER correctly. So
>>> all
>>>> that's left to do in this patch is to properly advertise this feature to L1.
>>>>
>>>> Note that vmcs12's VM_ENTRY/EXIT_LOAD_IA32_EFER are emulated by L0, by
>>> using
>>>> vmx_set_efer (which itself sets one of several vmcs02 fields), so we always
>>>> support this feature, regardless of whether the host supports it.
>>>>
>>>> Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
>>>> Signed-off-by: Jun Nakajima <jun.nakajima@intel.com>
>>>> Signed-off-by: Xinhao Xu <xinhao.xu@intel.com>
>>>> ---
>>>>  arch/x86/kvm/vmx.c | 23 ++++++++++++++++-------
>>>>  1 file changed, 16 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>> index 260a919..fb9cae5 100644
>>>> --- a/arch/x86/kvm/vmx.c
>>>> +++ b/arch/x86/kvm/vmx.c
>>>> @@ -2192,7 +2192,8 @@ static __init void nested_vmx_setup_ctls_msrs(void)
>>>>  #else
>>>>  	nested_vmx_exit_ctls_high = 0;
>>>>  #endif
>>>> -	nested_vmx_exit_ctls_high |=
>>> VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR;
>>>> +	nested_vmx_exit_ctls_high |=
>>> (VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
>>>> +				      VM_EXIT_LOAD_IA32_EFER);
>>>>
>>>>  	/* entry controls */
>>>>  	rdmsr(MSR_IA32_VMX_ENTRY_CTLS,
>>>> @@ -2201,8 +2202,8 @@ static __init void nested_vmx_setup_ctls_msrs(void)
>>>>  	nested_vmx_entry_ctls_low =
>>> VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR;
>>>>  	nested_vmx_entry_ctls_high &=
>>>>  		VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_IA32E_MODE;
>>>> -	nested_vmx_entry_ctls_high |=
>>> VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR;
>>>> -
>>>> +	nested_vmx_entry_ctls_high |=
>>> (VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR |
>>>> +				       VM_ENTRY_LOAD_IA32_EFER);
>>>>  	/* cpu-based controls */
>>>>  	rdmsr(MSR_IA32_VMX_PROCBASED_CTLS,
>>>>  		nested_vmx_procbased_ctls_low, nested_vmx_procbased_ctls_high);
>>>> @@ -7492,10 +7493,18 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu,
>>> struct vmcs12 *vmcs12)
>>>>  	vcpu->arch.cr0_guest_owned_bits &= ~vmcs12->cr0_guest_host_mask;
>>>>  	vmcs_writel(CR0_GUEST_HOST_MASK,
>>> ~vcpu->arch.cr0_guest_owned_bits);
>>>>
>>>> -	/* Note: IA32_MODE, LOAD_IA32_EFER are modified by vmx_set_efer
>>> below */
>>>> -	vmcs_write32(VM_EXIT_CONTROLS,
>>>> -		vmcs12->vm_exit_controls | vmcs_config.vmexit_ctrl);
>>>> -	vmcs_write32(VM_ENTRY_CONTROLS, vmcs12->vm_entry_controls |
>>>> +	/* L2->L1 exit controls are emulated - the hardware exit is to L0 so
>>>> +	 * we should use its exit controls. Note that IA32_MODE, LOAD_IA32_EFER
>>>> +	 * bits are further modified by vmx_set_efer() below.
>>>> +	 */
>>>> +	vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl);
>> This is wrong. We cannot use L0 exit control directly.
>> LOAD_PERF_GLOBAL_CTRL, LOAD_HOST_EFE, LOAD_HOST_PAT, ACK_INTR_ON_EXIT should use host's exit control. But others, still need use (vmcs12|host).
>>
> I do not see why. We always intercept DR7/PAT/EFER, so save is emulated
> too. Host address space size always come from L0 and preemption timer is
> not supported for nested IIRC and when it will be host will have to save
> it on exit anyway for correct emulation.

Preemption timer is already supported and works fine as far as I tested.
KVM doesn't use it for L1, so we do not need to save/restore it - IIRC.

Jan



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