linux-kernel - Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

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Message-ID: <jpgfudvgd3i.fsf@linux.bootlegged.copy>
Date:   Mon, 17 Jul 2017 13:58:09 -0400
From:   Bandan Das <bsd@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

Radim Krčmář <rkrcmar@...hat.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 ?

Thanks,
Bandan