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Date:   Mon, 4 Mar 2019 16:55:05 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     Fenghua Yu <fenghua.yu@intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
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Subject: Re: [PATCH v4 00/17] x86/split_lock: Enable #AC exception for split
 locked accesses
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References: <1551494711-213533-1-git-send-email-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?