From mboxrd@z Thu Jan  1 00:00:00 1970
From: will.deacon@arm.com (Will Deacon)
Date: Tue, 7 Jul 2015 11:24:06 +0100
Subject: [PATCH v3 08/11] KVM: arm: implement dirty bit mechanism for
 debug registers
In-Reply-To: <5A7DE9A0-E7A6-40B0-80F9-896F7DED0E47@linaro.org>
References: <1434969694-7432-1-git-send-email-zhichao.huang@linaro.org>
 <1434969694-7432-9-git-send-email-zhichao.huang@linaro.org>
 <20150630092020.GP11332@cbox>
 <B3B5AB0D-020C-483D-A6DE-76E355865010@linaro.org>
 <20150703115611.GB14220@lvm>
 <5A7DE9A0-E7A6-40B0-80F9-896F7DED0E47@linaro.org>
Message-ID: <20150707102405.GE23879@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, Jul 07, 2015 at 11:06:57AM +0100, Zhichao Huang wrote:
> Chazy and me are talking about how to reduce the saving/restoring
> overhead for debug registers.
> We want to add a state in hw_breakpoint.c to indicate whether the host
> enable any hwbrpts or not (might export a fuction that kvm can call),
> then we can read this state from memory instead of reading from real
> hardware registers, and to decide whether we need a world switch or
> not.
> Does it acceptable?

Maybe, hard to tell without the code. There are obvious races to deal with
if you use variables to indicate whether resources are in use -- why not
just trap debug access from the host as well? Then you could keep track of
the "owner" in kvm and trap accesses from everybody else.

Will