linux-kernel - Re: [PATCH] kvm/vmx: EPTP switching test

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Message-ID: <564AF21E.3010604@redhat.com>
Date:	Tue, 17 Nov 2015 10:23:42 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Kai Huang <kai.huang@...ux.intel.com>,
	Mihai Donțu <mdontu@...defender.com>,
	kvm@...r.kernel.org
Subject: Re: [PATCH] kvm/vmx: EPTP switching test

On 16/11/2015 19:18, =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= wrote:
>> > No idea how would I even test it, so I'm not interested in #VE at this
>> > point.  If you are - go ahead and post a patch for that on top though,
>> > why not.
> I thought that it's going to be simpler to provide functionality (that
> utilizes eptp switching) to the guest through #VE, which probably isn't
> true as I think more about it.  (Not interested in implementing it :])

#VE and EPTP switching are distinct features, one does not imply the other.

Unfortunately, EPTP switching is designed for a very specific use case
where the hypervisor is effectively part of the kernel, and the kernel
is trusted to some extent.  Examples include antivirus software and
virtual machines.  Antiviruses do use VMFUNC, that's as far as I know
the only current use case of it
(https://embedded.communities.intel.com/community/en/applications/blog/2013/06/13/roving-reporter-enhancing-retail-security-and-manageability-with-4th-generation-intel-core-processors).

So I'm against this patch, but only because I'm not sure why KVM would
ever use EPTP switching in its current incarnation.  The guest kernel is
absolutely not trusted by KVM.

Paolo
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