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

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Message-ID: <d7c03009-3b21-0bce-74f5-b11dd359eb97@arm.com>
Date:   Mon, 24 Apr 2017 10:33:29 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Hanjun Guo <guohanjun@...wei.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>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        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 24/04/17 10:14, 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 giving it a go. Catalin, can you queue this via the arm64 tree?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...