Re: [PATCH v4 00/17] x86/split_lock: Enable #AC exception for split locked accesses

From: Konrad Rzeszutek Wilk
Date: Mon Mar 04 2019 - 16:55:36 EST

> 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?