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

From: Bandan Das
Date: Tue Jul 11 2017 - 15:38:34 EST

Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx> writes:

> 2017-07-11 14:35-0400, Bandan Das:
>> Jim Mattson <jmattson@xxxxxxxxxx> 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.