linux-kernel - Re: [PATCH 1/5] KVM: nVMX: Fix VMX controls MSRs setup when nested VMX enabled

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Date:   Sat, 29 Aug 2020 10:51:47 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Chenyi Qiang <chenyi.qiang@...el.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] KVM: nVMX: Fix VMX controls MSRs setup when nested
 VMX enabled

On 8/29/2020 9:49 AM, Chenyi Qiang wrote:
> 
> 
> On 8/29/2020 1:43 AM, Jim Mattson wrote:
>> On Fri, Aug 28, 2020 at 1:54 AM Chenyi Qiang <chenyi.qiang@...el.com> 
>> wrote:
>>>
>>> KVM supports the nested VM_{EXIT, ENTRY}_LOAD_IA32_PERF_GLOBAL_CTRL and
>>> VM_{ENTRY_LOAD, EXIT_CLEAR}_BNDCFGS, but they doesn't expose during
>>> the setup of nested VMX controls MSR.
>>>
>>
>> Aren't these features added conditionally in
>> nested_vmx_entry_exit_ctls_update() and
>> nested_vmx_pmu_entry_exit_ctls_update()?
>>
> 
> Yes, but I assume vmcs_config.nested should reflect the global 
> capability of VMX MSR. KVM supports these two controls, so should be 
> exposed here.

No. I prefer to say they are removed conditionally in 
nested_vmx_entry_exit_ctls_update() and 
nested_vmx_pmu_entry_exit_ctls_update().

Userspace calls vmx_get_msr_feature() to query what KVM supports for 
these VMX MSR. In vmx_get_msr_feature(), it returns the value of 
vmcs_config.nested. As KVM supports these two bits, we should advertise 
them in vmcs_config.nested and report to userspace.