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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Liran Alon <liran.alon@oracle.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [PATCH] x86/kvm/nVMCS: fix VMCLEAR when Enlightened VMCS is in use
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References: <20190624133028.3710-1-vkuznets@redhat.com> <CEFF2A14-611A-417C-BC0A-8814862F26C6@oracle.com>
Date:   Tue, 25 Jun 2019 10:51:56 +0200
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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.

If you still dislike nested_enlightened_vmentry() having the side effect
of fetching evmcs_ptr I can get rid of it by splitting the function into
two, however, it will be less efficient for
nested_vmx_handle_enlightened_vmptrld(). Or we can just leave things as
they are there and use the newly introduced function in handle_vmclear()
only.

-- 
Vitaly