linux-kernel - Re: [PATCH v3 15/18] arm64: arch_timer: Enable CNTVCT

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Date:   Mon, 24 Apr 2017 11:18:01 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Hanjun Guo <guohanjun@...wei.com>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        "Lixiaoping (Timmy)" <lixiaoping3@...wei.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Scott Wood <oss@...error.net>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Dingtianhong <dingtianhong@...wei.com>,
        dann frazier <dann.frazier@...onical.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 15/18] arm64: arch_timer: Enable CNTVCT_EL0 trap if
 workaround is enabled

On Mon, Apr 24, 2017 at 05:14:29PM +0800, Hanjun Guo wrote:
> On 2017/4/24 16:40, Marc Zyngier wrote:
> > On 24/04/17 09:25, Lixiaoping (Timmy) wrote:
> >> Hi Marc,
> >>
> >> Sorry about previous email's confidential info. Please forget it.
> >>
> >> +#define ESR_ELx_SYS64_ISS_SYS_CNTFRQ	(ESR_ELx_SYS64_ISS_SYS_VAL(3, 3, 14, 0, 0) | \
> >> +					 ESR_ELx_SYS64_ISS_DIR_READ)
> >>
> >> I think (3, 3, 14, 0, 0) should be (3, 3, 0, 14, 0)?
> > Thanks for spotting this. I assumed that the sys_reg() and
> > SR_ELx_SYS64_ISS_SYS_VAL() macros took their arguments in the same 
> > order. That would have been too easy... ;-)
> >
> > Amended patch below, please let me know if it works for you.
> >
> > Thanks,
> >
> > 	M.
> >
> > >From 4444c86a97c1a487e12c319fdc197c88631d72b5 Mon Sep 17 00:00:00 2001
> > From: Marc Zyngier <marc.zyngier@....com>
> > Date: Mon, 24 Apr 2017 09:04:03 +0100
> > Subject: [PATCH] arm64: Add CNTFRQ_EL0 trap handler
> >
> > We now trap accesses to CNTVCT_EL0 when the counter is broken
> > enough to require the kernel to mediate the access. But it
> > turns out that some existing userspace (such as OpenMPI) do
> > probe for the counter frequency, leading to an UNDEF exception
> > as CNTVCT_EL0 and CNTFRQ_EL0 share the same control bit.
> >
> > The fix is to handle the exception the same way we do for CNTVCT_EL0.
> >
> > Fixes: a86bd139f2ae ("arm64: arch_timer: Enable CNTVCT_EL0 trap if workaround is enabled")
> > Reported-by: Hanjun Guo <guohanjun@...wei.com>
> > Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> > ---
> 
> I tested this patch and the undefined instruction error is gone, I can
> get the FREQ in the user space now, thank you very much for the quick
> response.
> 
> Tested-by: Hanjun Guo <guohanjun@...wei.com>
> Reviewed-by: Hanjun Guo <guohanjun@...wei.com>

Thanks for providing so quickly a fix and test it.

  -- Daniel

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