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Date: Wed, 19 Jul 2017 11:30:37 +0200
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
To: Bandan Das <bsd@redhat.com>
Cc: David Hildenbrand <david@redhat.com>, kvm@vger.kernel.org,
        pbonzini@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1
 hypervisor
Message-ID: <20170719093036.GA13079@potion>
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2017-07-17 13:58-0400, Bandan Das:
> Radim Krčmář <rkrcmar@redhat.com> writes:
> ...
>>> > and no other mentions of a VM exit, so I think that the VM exit happens
>>> > only under these conditions:
>>> >
>>> >   — The EPT memory type (bits 2:0) must be a value supported by the
>>> >     processor as indicated in the IA32_VMX_EPT_VPID_CAP MSR (see
>>> >     Appendix A.10).
>>> >   — Bits 5:3 (1 less than the EPT page-walk length) must be 3, indicating
>>> >     an EPT page-walk length of 4; see Section 28.2.2.
>>> >   — Bit 6 (enable bit for accessed and dirty flags for EPT) must be 0 if
>>> >     bit 21 of the IA32_VMX_EPT_VPID_CAP MSR (see Appendix A.10) is read
>>> >     as 0, indicating that the processor does not support accessed and
>>> >     dirty flags for EPT.
>>> >   — Reserved bits 11:7 and 63:N (where N is the processor’s
>>> >     physical-address width) must all be 0.
>>> >
>>> > And it looks like we need parts of nested_ept_init_mmu_context() to
>>> > properly handle VMX_EPT_AD_ENABLE_BIT.
>>> 
>>> I completely ignored AD and the #VE sections. I will add a TODO item
>>> in the comment section.
>>
>> AFAIK, we don't support #VE, but AD would be nice to handle from the
>> beginning.  (I think that caling nested_ept_init_mmu_context() as-is
>> isn't that bad.)
> 
> I went back to the spec to take a look at the AD handling. It doesn't look
> like anything needs to be done since nested_ept_init_mmu_context() is already
> being called with the correct eptp in prepare_vmcs02 ? Anything else that
> needs to be done for AD handling in vmfunc context ?

AD is decided by EPTP bit 6, so it can be toggled by EPTP switching and
we don't call prepare_vmcs02() after emulating VMFUNC vm exit.
We want to forward the new AD configuration to KVM's MMU.