linux-kernel - Re: [PATCH v2 1/2] KVM: VMX: Don't advertise EPT switching if EPT itself is not exposed

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Message-ID: <CANRm+Cw0vXAoK60XXB10C2A0LNvWqyy_5yzP6-kt466UF3sEpQ@mail.gmail.com>
Date:   Wed, 18 Oct 2017 09:05:10 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2 1/2] KVM: VMX: Don't advertise EPT switching if EPT
 itself is not exposed

2017-10-18 2:30 GMT+08:00 Jim Mattson <jmattson@...gle.com>:
> Similarly, it is legal for the IA32_VMX_VMFUNC MSR to report all-zero.
>
> For consistency, perhaps we should not clear the "enable VM functions"
> capability in the IA32_VMX_PROCBASED_CTLS2 MSR just because we do not
> support any VM functions.

Agreed.

Regards,
Wanpeng Li

>
> On Tue, Oct 17, 2017 at 10:35 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>> On 17/10/2017 19:29, Jim Mattson wrote:
>>> Following the same line of reasoning, what if
>>> vmx->nested.nested_vmx_secondary_ctls_high is 0 after clearing
>>> SECONDARY_EXEC_ENABLE_VMFUNC? Does it make sense to report
>>> CPU_BASED_ACTIVATE_SECONDARY_CONTROLS if we don't actually support any
>>> of the secondary controls?
>>
>> All-zero is a valid value for secondary controls, so I think yes.  Besides:
>>
>> 1) userspace can always get into a situation where there are no valid
>> secondary controls but processor-based execution controls have bit 31 as
>> 1-allowed;
>>
>> 2) I doubt that vmfunc can be the one bit that causes
>> nested_vmx_secondary_ctls_high to become zero :)
>>
>> Paolo