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From:   Bandan Das <bsd@redhat.com>
To:     Sean Christopherson <seanjc@google.com>
Cc:     Wei Huang <wei.huang2@amd.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, pbonzini@redhat.com,
        vkuznets@redhat.com, joro@8bytes.org, bp@alien8.de,
        tglx@linutronix.de, mingo@redhat.com, x86@kernel.org,
        jmattson@google.com, wanpengli@tencent.com, dgilbert@redhat.com,
        mlevitsk@redhat.com
Subject: Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions
References: <20210112063703.539893-1-wei.huang2@amd.com>
        <X/37QBMHxH8otaMa@google.com>
Date:   Tue, 12 Jan 2021 15:00:09 -0500
In-Reply-To: <X/37QBMHxH8otaMa@google.com> (Sean Christopherson's message of
        "Tue, 12 Jan 2021 11:40:48 -0800")
Message-ID: <jpgsg76kjsm.fsf@linux.bootlegged.copy>
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Sean Christopherson <seanjc@google.com> writes:
...
>> -	if ((emulation_type & EMULTYPE_VMWARE_GP) &&
>> -	    !is_vmware_backdoor_opcode(ctxt)) {
>> -		kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
>> -		return 1;
>> +	if (emulation_type & EMULTYPE_PARAVIRT_GP) {
>> +		vminstr = is_vm_instr_opcode(ctxt);
>> +		if (!vminstr && !is_vmware_backdoor_opcode(ctxt)) {
>> +			kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
>> +			return 1;
>> +		}
>> +		if (vminstr)
>> +			return vminstr;
>
> I'm pretty sure this doesn't correctly handle a VM-instr in L2 that hits a bad
> L0 GPA and that L1 wants to intercept.  The intercept bitmap isn't checked until
> x86_emulate_insn(), and the vm*_interception() helpers expect nested VM-Exits to
> be handled further up the stack.
>
So, the condition is that L2 executes a vmload and #GPs on a reserved address, jumps to L0 - L0 doesn't
check if L1 has asked for the instruction to be intercepted and goes on with emulating
vmload and returning back to L2 ?

>>  	}
>>  
>>  	/*
>> -- 
>> 2.27.0
>>