linux-kernel - Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors] page

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Message-ID: <20181025173242.GC30658@n2100.armlinux.org.uk>
Date:   Thu, 25 Oct 2018 18:32:42 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, linux-arm-kernel@...ts.infradead.org,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kim Phillips <kim.phillips@....com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        open list <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...hat.com>, l.stach@...gutronix.de
Subject: Re: [PATCH 2/2] perf tests: Add a test for the ARM 32-bit [vectors]
 page

On Thu, Oct 25, 2018 at 10:19:54AM -0700, Florian Fainelli wrote:
> On 10/24/18 7:10 PM, Andrew Lunn wrote:
> > On Wed, Oct 24, 2018 at 05:09:05PM -0700, Florian Fainelli wrote:
> >> perf on ARM requires CONFIG_KUSER_HELPERS to be turned on to allow some
> >> independance with respect to the ARM CPU being used. Add a test which
> >> tries to locate the [vectors] page, created when CONFIG_KUSER_HELPERS is
> >> turned on to help asses the system's health.
> > 
> > Hi Florian
> > 
> > I've suffered the pain from missing CONFIG_KUSER_HELPERS. The
> > segfaults give little clue as to what is going wrong,and gdb is not
> > much use either.
> 
> If you have a working backtrace, you can typically see the virtual
> address being in 0xffff_xxxx which gives a bit of a clue, but yes, this
> is not particularly helpful.
> 
> > 
> > What i don't see here is any clue to CONFIG_KUSER_HELPERS. If the test
> > fails, could you print a message suggesting CONFIG_KUSER_HELPERS on
> > ARM?
> 
> Sure, sounds reasonable, thanks for taking a look.

An alternative would be rather than adding this to user programs, to
have the kernel detect it and print a warning itself.

BTW, I note that the help text for CONFIG_KUSER_HELPERS needs to be
updated.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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