linux-kernel - Re: [PATCH 2/3 v2] KVM: nVMX: Enable VMFUNC for the L1 hypervisor

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Message-ID: <f0267f6f-673c-9175-1140-c9038a0031bc@redhat.com>
Date:   Mon, 10 Jul 2017 13:03:53 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Hildenbrand <david@...hat.com>, Bandan Das <bsd@...hat.com>,
        kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3 v2] KVM: nVMX: Enable VMFUNC for the L1 hypervisor

On 10/07/2017 11:17, David Hildenbrand wrote:
>> +
>> +	vmcs12 = get_vmcs12(vcpu);
>> +	if ((vmcs12->vm_function_control & (1 << function)) == 0)
> (learned that in c, shifting beyond the type size is undefined)
> 
> Should we check for function < 64 here? (as SDM mentions)

It should be already.  The manual says:

The VMFUNC instruction causes an invalid-opcode exception (#UD) if the
“enable VM functions” VM-execution controls is 0 1 or the value of EAX
is greater than 63 (only VM functions 0–63 can be enable). Otherwise,
the instruction causes a VM exit if the bit at position EAX is 0 in the
VM-function controls (the selected VM function is not enabled).

Paolo