linux-kernel - Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

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Message-ID: <1b90c04b-7c5a-80cb-0f28-5026cecf7f10@citrix.com>
Date:   Wed, 8 Apr 2020 10:52:12 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Peter Zijlstra <peterz@...radead.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, <hch@...radead.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        mingo <mingo@...hat.com>, bp <bp@...en8.de>, <hpa@...or.com>,
        x86 <x86@...nel.org>, "Kenneth R. Crudup" <kenny@...ix.com>,
        Jessica Yu <jeyu@...nel.org>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Tony Luck <tony.luck@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <jannh@...gle.com>, <keescook@...omium.org>,
        <David.Laight@...lab.com>, "Doug Covelli" <dcovelli@...are.com>,
        <mhiramat@...nel.org>
Subject: Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

On 08/04/2020 01:22, Paolo Bonzini wrote:
> On 08/04/20 01:15, Andrew Cooper wrote:
>>> Anyhow, I do not think it is the only use-case which is not covered by your
>>> patches (even considering CRs/DRs alone). For example, there is no kernel
>>> function to turn on CR4.VMXE, which is required to run hypervisors on x86.
>> How about taking this opportunity to see if there is a way to improve on
>> the status quo for co-existing hypervisor modules?
> Almost serious question: why?  I can understand VMware, but why can't at
> least VirtualBox use KVM on Linux?  I am not sure if they are still
> running device emulation in ring zero, but if so do you really want to
> do that these days?

I see a lot of good reasons not to use the VirtualBox out-of-tree module
specifically, but there are plenty of other out-of-tree hypervisors,
including Jailhouse and Bareflank which come to mind.

I'm not suggesting bending over backwards for them, but at the point
you're already breaking all of them anyway, it seems silly not to try
and address some of the other robustness issues.

~Andrew