linux-kernel - Re: [PATCH v3 2/2] KVM: VMX: Fix VPID capability detection

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Message-ID: <ff31dd1f-28ba-b7b3-7b56-333853706847@redhat.com>
Date:   Wed, 18 Oct 2017 17:40:17 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>, Wanpeng Li <kernellwp@...il.com>
Cc:     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 v3 2/2] KVM: VMX: Fix VPID capability detection

On 18/10/2017 17:39, Jim Mattson wrote:
> As long as we're taking the "better safe than sorry" approach, why
> don't we go ahead and clear vmx_capability.ept/vmx_capability.vpid
> along with the warnings?

Indeed.

Paolo

> On Tue, Oct 17, 2017 at 6:43 PM, Wanpeng Li <kernellwp@...il.com> wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> In my setup, EPT is not exposed to L1, the VPID capability is exposed and
>> can be observed by vmxcap tool in L1:
>> INVVPID supported                        yes
>> Individual-address INVVPID               yes
>> Single-context INVVPID                   yes
>> All-context INVVPID                      yes
>> Single-context-retaining-globals INVVPID yes
>>
>> However, the module parameter of VPID observed in L1 is always N, the
>> cpu_has_vmx_invvpid() check in L1 KVM fails since vmx_capability.vpid
>> is 0 and it is not read from MSR due to EPT is not exposed.
>>
>> The VPID can be used to tag linear mappings when EPT is not enabled. However,
>> current logic just detects VPID capability if EPT is enabled, 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:
>>  * add pr_warn_once
>> v1 -> v2:
>>  * rdmsr_safe instead of rdmsr
>>  * add more explanation to patch description
>>
>>  arch/x86/kvm/vmx.c | 13 ++++++++++---
>>  1 file changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 3644540..c14e981 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -3681,15 +3681,22 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
>>                                 SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
>>                                 SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY);
>>
>> +       rdmsr_safe(MSR_IA32_VMX_EPT_VPID_CAP,
>> +               &vmx_capability.ept, &vmx_capability.vpid);
>> +
>>         if (_cpu_based_2nd_exec_control & SECONDARY_EXEC_ENABLE_EPT) {
>>                 /* CR3 accesses and invlpg don't need to cause VM Exits when EPT
>>                    enabled */
>>                 _cpu_based_exec_control &= ~(CPU_BASED_CR3_LOAD_EXITING |
>>                                              CPU_BASED_CR3_STORE_EXITING |
>>                                              CPU_BASED_INVLPG_EXITING);
>> -               rdmsr(MSR_IA32_VMX_EPT_VPID_CAP,
>> -                     vmx_capability.ept, vmx_capability.vpid);
>> -       }
>> +       } else if (vmx_capability.ept)
>> +               pr_warn_once("EPT CAP should not exist if not support "
>> +                               "1-setting enable EPT VM-execution control\n");
>> +       if (!(_cpu_based_2nd_exec_control & SECONDARY_EXEC_ENABLE_VPID) &&
>> +               vmx_capability.vpid)
>> +               pr_warn_once("VPID CAP should not exist if not support "
>> +                               "1-setting enable VPID VM-execution control\n");
>>
>>         min = VM_EXIT_SAVE_DEBUG_CONTROLS | VM_EXIT_ACK_INTR_ON_EXIT;
>>  #ifdef CONFIG_X86_64
>> --
>> 2.7.4
>>