linux-kernel - Re: [PATCH 3/3] KVM: VMX: Extend VMX's #AC interceptor to handle split lock #AC in guest

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Message-ID: <87tv20lq7p.fsf@nanos.tec.linutronix.de>
Date:   Fri, 03 Apr 2020 14:16:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jim Mattson <jmattson@...gle.com>,
        "Kenneth R. Crudup" <kenny@...ix.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Nadav Amit <namit@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        x86 <x86@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jessica Yu <jeyu@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Doug Covelli <dcovelli@...are.com>
Subject: Re: [PATCH 3/3] KVM: VMX: Extend VMX's #AC interceptor to handle split lock #AC in guest

Jim,

Jim Mattson <jmattson@...gle.com> writes:
> On Thu, Apr 2, 2020 at 4:16 PM Kenneth R. Crudup <kenny@...ix.com> wrote:
>> On Thu, 2 Apr 2020, Steven Rostedt wrote:
>>
>> > If we go the approach of not letting VM modules load if it doesn't have the
>> > sld_safe flag set, how is this different than a VM module not loading due
>> > to kabi breakage?
>>
>> Why not a compromise: if such a module is attempted to be loaded, print up
>> a message saying something akin to "turn the parameter 'split_lock_detect'
>> off" as we reject loading it- and if we see that we've booted with it off
>> just splat a WARN_ON() if someone tries to load such modules?
>
> What modules are we talking about? I thought we were discussing L1
> hypervisors, which are just binary blobs. The only modules at the L0
> level are kvm and kvm_intel.

Maybe in your world, but VmWare (which got this started), VirtualBox,
Jailhouse and who knows what else _are_ L0 hypervisors. Otherwise we
wouldn't have that conversation at all.

Thanks,

        tglx