Re: [PATCH v2] KVM: nVMX: Fix read/write to MSR_IA32_FEATURE_CONTROL

[Gleb Natapov <gleb@redhat.com>]

On Fri, Jul 05, 2013 at 11:13:17PM +0800, Arthur Chunqi Li wrote:
> Fix read/write to IA32_FEATURE_CONTROL MSR in nested environment.
> 
> This patch simulate this MSR in nested_vmx and the default value is
> 0x0. BIOS should set it to 0x5 before VMXON. After setting the lock
> bit, write to it will cause #GP(0).
> 
> Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>
The patch is heavily based on Nadav's one. You need to preserve
authorship. Add From: and Nadav's Sign-off-by.

> ---
>  arch/x86/kvm/vmx.c |   25 +++++++++++++++++++++----
>  arch/x86/kvm/x86.c |    3 ++-
>  2 files changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 260a919..5e3d44e 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -373,6 +373,7 @@ struct nested_vmx {
>  	 * we must keep them pinned while L2 runs.
>  	 */
>  	struct page *apic_access_page;
> +	u64 msr_ia32_feature_control;
>  };
>  
>  #define POSTED_INTR_ON  0
> @@ -2277,8 +2278,11 @@ static int vmx_get_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
>  
>  	switch (msr_index) {
>  	case MSR_IA32_FEATURE_CONTROL:
> -		*pdata = 0;
> -		break;
> +		if (nested_vmx_allowed(vcpu)){
> +			*pdata = to_vmx(vcpu)->nested.msr_ia32_feature_control;
> +			break;
> +		}
> +		return 0;
>  	case MSR_IA32_VMX_BASIC:
>  		/*
>  		 * This MSR reports some information about VMX support. We
> @@ -2356,9 +2360,13 @@ static int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
>  	if (!nested_vmx_allowed(vcpu))
>  		return 0;
>  
> -	if (msr_index == MSR_IA32_FEATURE_CONTROL)
> -		/* TODO: the right thing. */
> +	if (msr_index == MSR_IA32_FEATURE_CONTROL){
> +		if (to_vmx(vcpu)->nested.msr_ia32_feature_control
> +				& FEATURE_CONTROL_LOCKED)
> +			return 0;
> +		to_vmx(vcpu)->nested.msr_ia32_feature_control = data;
You need to allow setting it from userspace, otherwise reset will not
clear it.

>  		return 1;
> +	}
>  	/*
>  	 * No need to treat VMX capability MSRs specially: If we don't handle
>  	 * them, handle_wrmsr will #GP(0), which is correct (they are readonly)
> @@ -5595,6 +5603,15 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
>  		skip_emulated_instruction(vcpu);
>  		return 1;
>  	}
> +
> +#define VMXON_NEEDED_FEATURES \
Avi asked to use const u64 here.

> +	  (FEATURE_CONTROL_LOCKED | FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX)
> +	if ((vmx->nested.msr_ia32_feature_control & VMXON_NEEDED_FEATURES)
> +			!= VMXON_NEEDED_FEATURES) {
> +		kvm_inject_gp(vcpu, 0);
> +		return 1;
> +	}
> +
>  	if (enable_shadow_vmcs) {
>  		shadow_vmcs = alloc_vmcs();
>  		if (!shadow_vmcs)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e8ba99c..2d4eb8e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -850,7 +850,8 @@ static u32 msrs_to_save[] = {
>  #ifdef CONFIG_X86_64
>  	MSR_CSTAR, MSR_KERNEL_GS_BASE, MSR_SYSCALL_MASK, MSR_LSTAR,
>  #endif
> -	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA
> +	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
> +	MSR_IA32_FEATURE_CONTROL
>  };
>  
>  static unsigned num_msrs_to_save;
> -- 
> 1.7.9.5

--
			Gleb.