linux-kernel - Re: [PATCH v2 2/3] KVM: VMX: Fix enable VPID even if INVVPID is not exposed in vmx capability

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Date:   Tue, 21 Mar 2017 09:50:05 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2 2/3] KVM: VMX: Fix enable VPID even if INVVPID is not
 exposed in vmx capability

On 21.03.2017 05:18, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> This can be reproduced by running L2 on L1, and disable VPID on L0 if w/o 
> commit "KVM: nVMX: Fix nested VPID vmx exec control", the L2 crash as below:
> 
> KVM: entry failed, hardware error 0x7
> EAX=00000000 EBX=00000000 ECX=00000000 EDX=000306c3
> ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000
> EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> ES =0000 00000000 0000ffff 00009300
> CS =f000 ffff0000 0000ffff 00009b00
> SS =0000 00000000 0000ffff 00009300
> DS =0000 00000000 0000ffff 00009300
> FS =0000 00000000 0000ffff 00009300
> GS =0000 00000000 0000ffff 00009300
> LDT=0000 00000000 0000ffff 00008200
> TR =0000 00000000 0000ffff 00008b00
> GDT=     00000000 0000ffff
> IDT=     00000000 0000ffff
> CR0=60000010 CR2=00000000 CR3=00000000 CR4=00000000
> DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
> DR6=00000000ffff0ff0 DR7=0000000000000400
> EFER=0000000000000000
> 
> Reference SDM 30.3 INVVPID:
>  
> Protected Mode Exceptions
> #UD 
>   - If not in VMX operation.
>   - If the logical processor does not support VPIDs (IA32_VMX_PROCBASED_CTLS2[37]=0).
>   - If the logical processor supports VPIDs (IA32_VMX_PROCBASED_CTLS2[37]=1) but does 
>     not support the INVVPID instruction (IA32_VMX_EPT_VPID_CAP[32]=0).
> 
> So we should check both VPID enable bit in vmx exec control and INVVPID support bit 
> in vmx capability MSRs to enable VPID. This patch adds the guarantee to not enable VPID
> if INVVPID is not exposed in vmx capability MSRs.
> 

Makes sense to me. Wonder how many systems are out there that have VPID
but not INVVPID? Or will this never happen on real hardware?

> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  arch/x86/kvm/vmx.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 06d8080..b310214 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1239,6 +1239,11 @@ static inline bool cpu_has_vmx_invvpid_global(void)
>  	return vmx_capability.vpid & VMX_VPID_EXTENT_GLOBAL_CONTEXT_BIT;
>  }
>  
> +static inline bool cpu_has_vmx_invvpid(void)
> +{
> +	return vmx_capability.vpid & VMX_VPID_INVVPID_BIT;
> +}
> +
>  static inline bool cpu_has_vmx_ept(void)
>  {
>  	return vmcs_config.cpu_based_2nd_exec_ctrl &
> @@ -6519,8 +6524,10 @@ static __init int hardware_setup(void)
>  	if (boot_cpu_has(X86_FEATURE_NX))
>  		kvm_enable_efer_bits(EFER_NX);
>  
> -	if (!cpu_has_vmx_vpid())
> +	if (!cpu_has_vmx_vpid() ||
> +		!(cpu_has_vmx_invvpid()))

This indentation looks weird. Can't this be fit into one line?

>  		enable_vpid = 0;
> +

unrelated change

>  	if (!cpu_has_vmx_shadow_vmcs())
>  		enable_shadow_vmcs = 0;
>  	if (enable_shadow_vmcs)
> 


-- 

Thanks,

David