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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH 1/2] KVM: x86: Emulate split-lock access as a write
Date:   Thu, 30 Jan 2020 07:16:24 -0800
Message-Id: <777C5046-B9DE-4F8C-B04F-28A546AE4A3F@amacapital.net>
References: <db3b854fd03745738f46cfce451d9c98@AcuMS.aculab.com>
Cc:     Xiaoyao Li <xiaoyao.li@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
In-Reply-To: <db3b854fd03745738f46cfce451d9c98@AcuMS.aculab.com>
To:     David Laight <David.Laight@aculab.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Jan 30, 2020, at 4:31 AM, David Laight <David.Laight@aculab.com> wrote:=

>=20
> =EF=BB=BFFrom: 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.
>>=20
>> 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.
>=20
> 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.
>=20
>   =20

The existing page-spanning case is just as wrong.=