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

[Paolo Bonzini <pbonzini@redhat.com>]

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);
> +
> +	/* vmcs12's VM_ENTRY_LOAD_IA32_EFER and VM_ENTRY_IA32E_MODE are
> +	 * emulated by vmx_set_efer(), below.

VM_ENTRY_LOAD_IA32_EFER is not emulated by vmx_set_efer, so:

    /* vmcs12's VM_ENTRY_LOAD_IA32_EFER and VM_ENTRY_IA32E_MODE
     * are emulated below.  VM_ENTRY_IA32E_MODE is handled in
     * vmx_set_efer().  */

Paolo

> +	 */
> +	vmcs_write32(VM_ENTRY_CONTROLS,
> +		(vmcs12->vm_entry_controls & ~VM_ENTRY_LOAD_IA32_EFER &
> +			~VM_ENTRY_IA32E_MODE) |
>  		(vmcs_config.vmentry_ctrl & ~VM_ENTRY_IA32E_MODE));
>  
>  	if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PAT)
>