linux-kernel - Re: [RFC 7/7] KVM: VMX: Enable PKS for nested VM

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Date:   Fri, 14 Aug 2020 18:07:52 +0800
From:   Chenyi Qiang <chenyi.qiang@...el.com>
To:     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>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 7/7] KVM: VMX: Enable PKS for nested VM



On 8/14/2020 1:52 AM, Jim Mattson wrote:
> On Wed, Aug 12, 2020 at 9:54 PM Chenyi Qiang <chenyi.qiang@...el.com> wrote:
>>
>>
>>
>> On 8/11/2020 8:05 AM, Jim Mattson wrote:
>>> On Fri, Aug 7, 2020 at 1:47 AM Chenyi Qiang <chenyi.qiang@...el.com> wrote:
>>>>
>>>> PKS MSR passes through guest directly. Configure the MSR to match the
>>>> L0/L1 settings so that nested VM runs PKS properly.
>>>>
>>>> Signed-off-by: Chenyi Qiang <chenyi.qiang@...el.com>
>>>> ---
> 
>>>> +           (!vmx->nested.nested_run_pending ||
>>>> +            !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PKRS)))
>>>> +               vmcs_write64(GUEST_IA32_PKRS, vmx->nested.vmcs01_guest_pkrs);
>>>
>>> This doesn't seem right to me. On the target of a live migration, with
>>> L2 active at the time the snapshot was taken (i.e.,
>>> vmx->nested.nested_run_pending=0), it looks like we're going to try to
>>> overwrite the current L2 PKRS value with L1's PKRS value (except that
>>> in this situation, vmx->nested.vmcs01_guest_pkrs should actually be
>>> 0). Am I missing something?
>>>
>>
>> We overwrite the L2 PKRS with L1's value when L2 doesn't support PKS.
>> Because the L1's VM_ENTRY_LOAD_IA32_PKRS is off, we need to migrate L1's
>> PKRS to L2.
> 
> I'm thinking of the case where vmx->nested.nested_run_pending is
> false, and we are processing a KVM_SET_NESTED_STATE ioctl, yet
> VM_ENTRY_LOAD_IA32_PKRS *is* set in the vmcs12.
> 

Oh, I miss this case. What I'm still confused here is that the 
restoration for GUEST_IA32_DEBUGCTL and GUEST_BNDCFGS have the same 
issue, right? or I miss something.