linux-kernel - Re: [PATCH v3 1/2] KVM: nVMX: Fix EPT switching advertising

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Date:   Wed, 18 Oct 2017 17:36:20 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v3 1/2] KVM: nVMX: Fix EPT switching advertising

2017-10-18 17:31 GMT+08:00 David Hildenbrand <david@...hat.com>:
> On 18.10.2017 03:42, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> I can use vmxcap tool to observe "EPTP Switching   yes" even if EPT is not
>> exposed to L1.
>>
>> EPT switching is advertised unconditionally since it is emulated, however,
>> it can be treated as an extended feature for EPT and it should not be
>> advertised if EPT itself is not exposed. This patch fixes it.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Jim Mattson <jmattson@...gle.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>> v2 -> v3:
>>  * it is legal for the IA32_VMX_VMFUNC MSR to report all-zero
>> v1 -> v2:
>>  * don't advertise "EPT VM Functions" in secondary processor-based VM-execution
>>    controls if we don't actually support any VM Functions.
>>
>>  arch/x86/kvm/vmx.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index c460b0b..3644540 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2842,8 +2842,9 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
>>                * Advertise EPTP switching unconditionally
>>                * since we emulate it
>>                */
>> -             vmx->nested.nested_vmx_vmfunc_controls =
>> -                     VMX_VMFUNC_EPTP_SWITCHING;
>> +             if (enable_ept)
>> +                     vmx->nested.nested_vmx_vmfunc_controls =
>> +                             VMX_VMFUNC_EPTP_SWITCHING;
>>       }
>>
>>       /*
>>
>
> I think we talked about how that cannot happen. But you observe it, so
> it seems to happen :)

It is very easy to reproduce if you run L1 w/ ept=0.

Regards,
Wanpeng Li