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From: Bandan Das <bsd@redhat.com>
To: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc: Jim Mattson <jmattson@google.com>,
        David Hildenbrand <david@redhat.com>, kvm list <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor
References: <20170710204936.4001-1-bsd@redhat.com>
        <20170710204936.4001-4-bsd@redhat.com>
        <2d50ebc4-9328-ce08-b55b-6a331ee13cc3@redhat.com>
        <jpgy3ruam9i.fsf@linux.bootlegged.copy>
        <CALMp9eQyWQyyyP=K1+HieiQJHvBFzMEFGufOz6BFgb-mmdQm=Q@mail.gmail.com>
        <jpga84ayg8b.fsf@linux.bootlegged.copy> <20170711191334.GB3442@potion>
Date: Tue, 11 Jul 2017 15:38:14 -0400
In-Reply-To: <20170711191334.GB3442@potion> ("Radim \=\?utf-8\?B\?S3LEjW3DocWZ\?\=
 \=\?utf-8\?B\?Iidz\?\= message of "Tue,
        11 Jul 2017 21:13:34 +0200")
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Radim Krčmář <rkrcmar@redhat.com> writes:

> 2017-07-11 14:35-0400, Bandan Das:
>> Jim Mattson <jmattson@google.com> writes:
>> ...
>> >>> I can find the definition for an vmexit in case of index >=
>> >>> VMFUNC_EPTP_ENTRIES, but not for !vmcs12->eptp_list_address in the SDM.
>> >>>
>> >>> Can you give me a hint?
>> >>
>> >> I don't think there is. Since, we are basically emulating eptp switching
>> >> for L2, this is a good check to have.
>> >
>> > There is nothing wrong with a hypervisor using physical page 0 for
>> > whatever purpose it likes, including an EPTP list.
>> 
>> Right, but of all the things, a l1 hypervisor wanting page 0 for a eptp list
>> address most likely means it forgot to initialize it. Whatever damage it does will
>> still end up with vmfunc vmexit anyway.
>
> Most likely, but not certainly.  I also don't see a to diverge from the
> spec here.

Actually, this is a specific case where I would like to diverge from the spec.
But then again, it's L1 shooting itself in the foot and this would be a rarely
used code path, so, I am fine removing it.