linux-kernel - RE: [PATCH 1/2] KVM: x86: Emulate split-lock access as a write

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Date:   Thu, 30 Jan 2020 12:31:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Xiaoyao Li' <xiaoyao.li@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Sean Christopherson" <sean.j.christopherson@...el.com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [PATCH 1/2] KVM: x86: Emulate split-lock access as a write

From: Xiaoyao Li
> Sent: 30 January 2020 12:20
> If split lock detect is enabled (warn/fatal), #AC handler calls die()
> when split lock happens in kernel.
> 
> A sane guest should never tigger emulation on a split-lock access, but
> it cannot prevent malicous guest from doing this. So just emulating the
> access as a write if it's a split-lock access to avoid malicous guest
> polluting the kernel log.

That doesn't seem right if, for example, the locked access is addx.
ISTM it would be better to force an immediate fatal error of some
kind than just corrupt the guest memory.

	David

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