linux-kernel - Re: [PATCH] KVM: nVMX: set rflags to specify success in handle

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Date:   Thu, 23 Jan 2020 10:23:42 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        linmiaohe <linmiaohe@...wei.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        rkrcmar@...hat.com, sean.j.christopherson@...el.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com
Subject: Re: [PATCH] KVM: nVMX: set rflags to specify success in
 handle_invvpid() default case

On 23/01/20 09:55, Vitaly Kuznetsov wrote:
>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>> index 7608924ee8c1..985d3307ec56 100644
>> --- a/arch/x86/kvm/vmx/nested.c
>> +++ b/arch/x86/kvm/vmx/nested.c
>> @@ -5165,7 +5165,7 @@ static int handle_invvpid(struct kvm_vcpu *vcpu)
>>  		break;
>>  	default:
>>  		WARN_ON_ONCE(1);
>> -		return kvm_skip_emulated_instruction(vcpu);
>> +		break;
>>  	}
>>  
>>  	return nested_vmx_succeed(vcpu);
> Your patch seems to do the right thing, however, I started wondering if
> WARN_ON_ONCE() is the right thing to do. SDM says that "If an
> unsupported INVVPID type is specified, the instruction fails." and this
> is similar to INVEPT and I decided to check what handle_invept()
> does. Well, it does BUG_ON(). 
> 
> Are we doing the right thing in any of these cases?

Yes, both INVEPT and INVVPID catch this earlier.

For INVEPT:

        types = (vmx->nested.msrs.ept_caps >> VMX_EPT_EXTENT_SHIFT) & 6;

        if (type >= 32 || !(types & (1 << type)))
                return nested_vmx_failValid(vcpu,
                                VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);



For INVVPID:

        types = (vmx->nested.msrs.vpid_caps &
                        VMX_VPID_EXTENT_SUPPORTED_MASK) >> 8;

        if (type >= 32 || !(types & (1 << type)))
                return nested_vmx_failValid(vcpu,
                        VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);

So I'm leaning towards not applying Miaohe's patch.  Happy Mouse Year
to everyone, here is an ASCII art (except for one Unicode character) mouse:


       __()()
      /     o)
  ~~~~\_,__,_>°

Thanks,