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Date:   Wed, 16 Oct 2019 08:41:16 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Xiaoyao Li <xiaoyao.li@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        linux-kernel <linux-kernel@vger.kernel.org>,
        x86 <x86@kernel.org>, kvm@vger.kernel.org
Subject: Re: [PATCH v9 09/17] x86/split_lock: Handle #AC exception for split
 lock
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On Wed, Oct 16, 2019 at 04:08:14PM +0200, Paolo Bonzini wrote:
> SIGBUS (actually a new KVM_EXIT_INTERNAL_ERROR result from KVM_RUN is
> better, but that's the idea) is for when you're debugging guests.
> Global disable (or alternatively, disable SMT) is for production use.

Alternatively, for guests without split-lock #AC enabled, what if KVM were
to emulate the faulting instruction with split-lock detection temporarily
disabled?

The emulator can presumably handle all such lock instructions, and an
unhandled instruction would naturally exit to userspace.

The latency of VM-Enter+VM-Exit should be enough to guard against DoS from
a malicious guest.  KVM could also artificially rate-limit a guest that is
generating copious amounts of split-lock #ACs.