From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH v4 00/17] x86/split_lock: Enable #AC exception for split
 locked accesses
Date: Mon, 4 Mar 2019 16:55:05 -0500
Message-ID: <20190304215505.GC30350@char.us.oracle.com>
References: <1551494711-213533-1-git-send-email-fenghua.yu@intel.com>
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Cc: 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>,
        Dave Hansen <dave.hansen@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        Xiaoyao Li <xiaoyao.li@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        x86 <x86@kernel.org>, kvm@vger.kernel.org
To: Fenghua Yu <fenghua.yu@intel.com>
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> This capability may also find usage in cloud. A user process with split
> lock running in one guest can block other cores from accessing shared
> memory during its split locked memory access. That may cause overall
> system performance degradation.

"shared memory" ? As in memory shared between two guests?

> 
> Split lock may open a security hole where malicious user code may slow
> down overall system by executing instructions with split lock.

How much slowdown are we talking?