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

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Date:   Thu, 25 Oct 2018 19:03:32 +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 10:53:12AM -0700, Florian Fainelli wrote:
> Something like this below? It does not have to be an alternative
> solution, I would find it useful for perf to make sure the vectors page
> is present in the virtual address space by having an explicit test. perf
> maintains, what do you think?

Yep, I'd swap the two tests merely because the check for 'sig' will be
slightly cheaper than the mask-and-test of addr, but it probably doesn't
make that much difference.

> 
> diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
> index f4ea4c62c613..b045b48d368d 100644
> --- a/arch/arm/mm/fault.c
> +++ b/arch/arm/mm/fault.c
> @@ -173,6 +173,11 @@ __do_user_fault(struct task_struct *tsk, unsigned
> long addr,
>                 show_regs(regs);
>         }
>  #endif
> +#ifndef CONFIG_KUSER_HELPERS
> +       if (((addr & PAGE_MASK) == 0xffff0000) && (sig == SIGSEGV))
> +               printk(KERN_DEBUG "%s: CONFIG_KUSER_HELPERS disabled at
> 0x%08lx\n",
> +                      tsk->comm, addr);
> +#endif
> 
>         tsk->thread.address = addr;
>         tsk->thread.error_code = fsr;
> 
> 
> > 
> > BTW, I note that the help text for CONFIG_KUSER_HELPERS needs to be
> > updated.
> > 
> 
> 
> -- 
> Florian

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