linux-kernel - Re: [PATCH] ARM: hw_breakpoint: Handle inexact watchpoint addresses

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Message-ID: <20191120191813.GD4799@willie-the-truck>
Date:   Wed, 20 Nov 2019 19:18:13 +0000
From:   Will Deacon <will@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Pavel Labath <labath@...gle.com>,
        Pratyush Anand <panand@...hat.com>, mka@...omium.org,
        kinaba@...gle.com, Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: hw_breakpoint: Handle inexact watchpoint addresses

On Sat, Oct 19, 2019 at 11:12:26AM -0700, Douglas Anderson wrote:
> This is commit fdfeff0f9e3d ("arm64: hw_breakpoint: Handle inexact
> watchpoint addresses") but ported to arm32, which has the same
> problem.
> 
> This problem was found by Android CTS tests, notably the
> "watchpoint_imprecise" test [1].  I tested locally against a copycat
> (simplified) version of the test though.
> 
> [1] https://android.googlesource.com/platform/bionic/+/master/tests/sys_ptrace_test.cpp
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
>  arch/arm/kernel/hw_breakpoint.c | 96 ++++++++++++++++++++++++---------
>  1 file changed, 70 insertions(+), 26 deletions(-)

Sorry for taking so long to look at this. After wrapping my head around the
logic again, I think it looks fine, so please put it into the patch system
with my Ack:

Acked-by: Will Deacon <will@...nel.org>

One interesting difference between the implementation here and the arm64
code is that I think if you have multiple watchpoints, all of which fire
with a distance != 0, then arm32 will actually report them all whereas
you'd only get one on arm64.

Will