From: Liran Alon <liran.alon@oracle.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH] x86/kvm/nVMCS: fix VMCLEAR when Enlightened VMCS is in use
Date: Tue, 25 Jun 2019 14:18:05 +0300 [thread overview]
Message-ID: <702DE49A-0ED0-4012-B702-F4759B11B1AE@oracle.com> (raw)
In-Reply-To: <87ftnxex1g.fsf@vitty.brq.redhat.com>
> On 25 Jun 2019, at 14:15, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Liran Alon <liran.alon@oracle.com> writes:
>
>>> On 25 Jun 2019, at 11:51, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>>>
>>> Liran Alon <liran.alon@oracle.com> writes:
>>>
>>>>> On 24 Jun 2019, at 16:30, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>>>>>
>>>>>
>>>>> +bool nested_enlightened_vmentry(struct kvm_vcpu *vcpu, u64 *evmptr)
>>>>
>>>> I prefer to rename evmptr to evmcs_ptr. I think it’s more readable and sufficiently short.
>>>> In addition, I think you should return either -1ull or assist_page.current_nested_vmcs.
>>>> i.e. Don’t return evmcs_ptr by pointer but instead as a return-value
>>>> and get rid of the bool.
>>>
>>> Actually no, sorry, I'm having second thoughts here: in handle_vmclear()
>>> we don't care about the value of evmcs_ptr, we only want to check that
>>> enlightened vmentry bit is enabled in assist page. If we switch to
>>> checking evmcs_ptr against '-1', for example, we will make '-1' a magic
>>> value which is not in the TLFS. Windows may decide to use it for
>>> something else - and we will get a hard-to-debug bug again.
>>
>> I’m not sure I understand.
>> You are worried that when guest have setup a valid assist-page and set
>> enlighten_vmentry to true,
>> that assist_page.current_nested_vmcs can be -1ull and still be considered a valid eVMCS?
>> I don't think that's reasonable.
>
> No, -1ull is not a valid eVMCS - but this shouldn't change VMCLEAR
> semantics as VMCLEAR has it's own argument. It's perfectly valid to try
> to put a eVMCS which was previously used on a different vCPU (and thus
> which is 'active') to non-active state. The fact that we don't have an
> active eVMCS on the vCPU doing VMCLEAR shouldn't matter at all.
>
> --
> Vitaly
Oh oops sure. Yes you are right.
I forgot about the larger context here for a moment.
Sorry for the confusion. :)
-Liran
prev parent reply other threads:[~2019-06-25 11:18 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-24 13:30 [PATCH] x86/kvm/nVMCS: fix VMCLEAR when Enlightened VMCS is in use Vitaly Kuznetsov
2019-06-24 13:41 ` Liran Alon
2019-06-24 14:16 ` Vitaly Kuznetsov
2019-06-24 14:45 ` Liran Alon
2019-06-26 9:39 ` Vitaly Kuznetsov
2019-06-26 12:10 ` Paolo Bonzini
2019-06-25 8:51 ` Vitaly Kuznetsov
2019-06-25 11:01 ` Liran Alon
2019-06-25 11:15 ` Vitaly Kuznetsov
2019-06-25 11:18 ` Liran Alon [this message]
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