linux-kernel - Re: [PATCH v2 10/21] KVM:x86: Add #CP support in guest exception classification

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Message-ID: <7bf51510-ca6e-d4b2-31bf-405258fd08e7@intel.com>
Date:   Thu, 4 May 2023 11:41:17 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
CC:     <rick.p.edgecombe@...el.com>, <seanjc@...gle.com>,
        <pbonzini@...hat.com>, <peterz@...radead.org>,
        <john.allen@....com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/21] KVM:x86: Add #CP support in guest exception
 classification


On 4/28/2023 2:09 PM, Binbin Wu wrote:
>
>
> On 4/21/2023 9:46 PM, Yang Weijiang wrote:
>> Add handling for Control Protection (#CP) exceptions(vector 21).
>> The new vector is introduced for Intel's Control-Flow Enforcement
>> Technology (CET) relevant violation cases.
>> See Intel's SDM for details.
>>
[...]
>>   -static int exception_class(int vector)
>> +static int exception_class(struct kvm_vcpu *vcpu, int vector)
>>   {
>>       switch (vector) {
>>       case PF_VECTOR:
>>           return EXCPT_PF;
>> +    case CP_VECTOR:
>> +        if (vcpu->arch.cr4_guest_rsvd_bits & X86_CR4_CET)
>> +            return EXCPT_BENIGN;
>> +        return EXCPT_CONTRIBUTORY;
> By definition, #CP is Contributory.
> Can you explain more about this change here which treats #CP as 
> EXCPT_BENIGN when CET is not enabled in guest?

I check the history of this patch, found maintainer modified the patch 
due to some unit test issue in L1. You can check the

details here:

Re: [PATCH v15 04/14] KVM: x86: Add #CP support in guest exception 
dispatch - Sean Christopherson (kernel.org) 
<https://lore.kernel.org/all/YBsZwvwhshw+s7yQ@google.com/>


>
> In current KVM code, there is suppose no #CP triggered in guest if CET 
> is not enalbed in guest, right?

Yes.

>>       case DE_VECTOR:
>>       case TS_VECTOR:
>>       case NP_VECTOR:


[...]