linux-kernel - Re: [RFC PATCH 4/4] KVM: vmx: add support for emulating UMIP

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Date:	Wed, 13 Jul 2016 12:21:52 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Yang Zhang <yang.zhang.wz@...il.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [RFC PATCH 4/4] KVM: vmx: add support for emulating UMIP



On 13/07/2016 12:02, Yang Zhang wrote:
> On 2016/7/13 17:35, Paolo Bonzini wrote:
>>
>>
>> On 13/07/2016 11:21, Yang Zhang wrote:
>>>>
>>>> +static int handle_desc(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +    WARN_ON(!(vcpu->arch.cr4 & X86_CR4_UMIP));
>>>
>>> I think WARN_ON is too heavy since a malicious guest may trigger it
>>> always.
>>
>> I missed this---how so?  Setting the bit is under "if ((cr4 &
>> X86_CR4_UMIP) && !boot_cpu_has(X86_FEATURE_UMIP))".
> 
> Sorry, I consider it under my previous suggestion(setting it
> unconditionally). :(

No problem, thanks for your interest!

Paolo