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Subject: Re: [PATCH v3] irqchip/gic-v3: Ensure GICR_CTLR.EnableLPI=0 is
 observed before enabling
To:     Marc Zyngier <marc.zyngier@arm.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Vikram Sethi <vikrams@codeaurora.org>
References: <1521683929-15644-1-git-send-email-shankerd@codeaurora.org>
 <d1161c2d-e16d-14e6-5450-be26d348100d@arm.com>
From:   Shanker Donthineni <shankerd@codeaurora.org>
Message-ID: <8087e009-4eca-ab92-cbca-23ccfb3fafac@codeaurora.org>
Date:   Thu, 22 Mar 2018 14:41:09 -0500
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Hi Marc,

On 03/22/2018 10:51 AM, Marc Zyngier wrote:
> On 22/03/18 01:58, Shanker Donthineni wrote:
>> The definition of the GICR_CTLR.RWP control bit was expanded to indicate
>> status of changing GICR_CTLR.EnableLPI from 1 to 0 is being in progress
>> or completed. Software must observe GICR_CTLR.RWP==0 after clearing
>> GICR_CTLR.EnableLPI from 1 to 0 and before writing GICR_PENDBASER and/or
>> GICR_PROPBASER, otherwise behavior is UNPREDICTABLE.
>>
>> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
>> ---
>> Changes since v2:
>>   -Revert readl_relaxed_poll() usage since it's not usable in GICv3 probe().
>>   -Changes to pr_xxx messages.
>>
>> Changes since v1:
>>   -Moved LPI disable code to a seperate function as Marc suggested.
>>   -Mark's suggestion to use readl_relaxed_poll_timeout() helper functions.
>>
>>  drivers/irqchip/irq-gic-v3-its.c   | 75 +++++++++++++++++++++++++++++++-------
>>  include/linux/irqchip/arm-gic-v3.h |  1 +
>>  2 files changed, 62 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 2cbb19c..c1e8a8e 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -33,6 +33,7 @@
>>  #include <linux/of_platform.h>
>>  #include <linux/percpu.h>
>>  #include <linux/slab.h>
>> +#include <linux/time64.h>
>>  
>>  #include <linux/irqchip.h>
>>  #include <linux/irqchip/arm-gic-v3.h>
> 
> This hunk doesn't apply to my -next branch, but I don't think it is
> actually required either...
> 

I'll try to drop "#include <linux/time64.h>" in next patch if USEC_PER_SEC
included by other header files or rebase to -next branch.

>> @@ -1875,16 +1876,6 @@ static void its_cpu_init_lpis(void)
>>  		gic_data_rdist()->pend_page = pend_page;
>>  	}
>>  
>> -	/* Disable LPIs */
>> -	val = readl_relaxed(rbase + GICR_CTLR);
>> -	val &= ~GICR_CTLR_ENABLE_LPIS;
>> -	writel_relaxed(val, rbase + GICR_CTLR);
>> -
>> -	/*
>> -	 * Make sure any change to the table is observable by the GIC.
>> -	 */
>> -	dsb(sy);
>> -
>>  	/* set PROPBASE */
>>  	val = (page_to_phys(gic_rdists->prop_page) |
>>  	       GICR_PROPBASER_InnerShareable |
>> @@ -3287,13 +3278,69 @@ static bool gic_rdists_supports_plpis(void)
>>  	return !!(gic_read_typer(gic_data_rdist_rd_base() + GICR_TYPER) & GICR_TYPER_PLPIS);
>>  }
>>  
>> +static int redist_disable_lpis(void)
>> +{
>> +	void __iomem *rbase = gic_data_rdist_rd_base();
>> +	u64 timeout = USEC_PER_SEC;
>> +	u64 val;
>> +
>> +	if (!gic_rdists_supports_plpis()) {
>> +		pr_info("CPU%d: LPIs not supported\n", smp_processor_id());
>> +		return -ENXIO;
>> +	}
>> +
>> +	val = readl_relaxed(rbase + GICR_CTLR);
>> +	if (!(val & GICR_CTLR_ENABLE_LPIS))
>> +		return 0;
>> +
>> +	pr_warn("CPU%d: Booted with LPIs enabled, memory probably corrupted\n",
>> +		smp_processor_id());
>> +	add_taint(TAINT_CRAP, LOCKDEP_STILL_OK);
>> +
>> +	/* Disable LPIs */
>> +	val &= ~GICR_CTLR_ENABLE_LPIS;
>> +	writel_relaxed(val, rbase + GICR_CTLR);
>> +
>> +	/* Make sure any change to GICR_CTLR is observable by the GIC */
>> +	dsb(sy);
>> +
>> +	/**
>> +	 * Software must observe RWP==0 after clearing GICR_CTLR.EnableLPIs
>> +	 * from 1 to 0 before programming GICR_PEND{PROP}BASER registers.
>> +	 * Bail out the driver probe() in case of timeout.
>> +	 */
>> +	while (readl_relaxed(rbase + GICR_CTLR) & GICR_CTLR_RWP) {
>> +		if (!timeout) {
>> +			pr_err("CPU%d: Failed to observe RWP==0 after disabling LPIs\n",
> 
> I think you can simplify the message with something like:
> 
> 	"Time-out disabling LPIs\n"
> 
> Nobody apart from you and I really want to know about RWP...
> 

I'll change.

>> +			       smp_processor_id());
>> +			return -ETIMEDOUT;
>> +		}
>> +		udelay(1);
>> +		timeout--;
>> +	}
>> +
>> +	/**
>> +	 * After it has been written to 1, it is IMPLEMENTATION DEFINED whether
>> +	 * the bit GICR_CTLR.EnableLPI becomes RES1 or can be cleared to 0.
>> +	 * Bail out the driver probe() on systems where it's RES1.
>> +	 */
>> +	if (readl_relaxed(rbase + GICR_CTLR) & GICR_CTLR_ENABLE_LPIS) {
>> +		pr_err("CPU%d: Failed to disable LPIs\n", smp_processor_id());
>> +		return -EBUSY;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  int its_cpu_init(void)
>>  {
>>  	if (!list_empty(&its_nodes)) {
>> -		if (!gic_rdists_supports_plpis()) {
>> -			pr_info("CPU%d: LPIs not supported\n", smp_processor_id());
>> -			return -ENXIO;
>> -		}
>> +		int ret;
>> +
>> +		ret = redist_disable_lpis();
>> +		if (ret)
>> +			return ret;
> 
> Just realised that this is totally broken.
> 
> Why do we have this in the loop? Checking the LPI support for each ITS
> was admittedly braindead (we only need to check it once per CPU), but
> now trying to disable the LPIs each time we encounter an ITS is going to
> make it go crazy and taint the kernel for no reason.
> 

Sorry, I didn't quite understand suggestions you're recommending. I don't
see any loop here, it just checks the ITS_LIST_EMPTY.

The function its_cpu_init() is being called for each CPU coming online.
We're trying to disable GICR LPI before calling its_cpu_init_lpis() and
its_cpu_init_collection(). Newly added function redist_disable_lpis()
will be called only once per CPU but not per each ITS hardware instance.
Is something I'm missing here?

>> +
>>  		its_cpu_init_lpis();
>>  		its_cpu_init_collection();
>>  	}
>> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
>> index b26eccc..c6f4c48 100644
>> --- a/include/linux/irqchip/arm-gic-v3.h
>> +++ b/include/linux/irqchip/arm-gic-v3.h
>> @@ -106,6 +106,7 @@
>>  #define GICR_PIDR2			GICD_PIDR2
>>  
>>  #define GICR_CTLR_ENABLE_LPIS		(1UL << 0)
>> +#define GICR_CTLR_RWP			(1UL << 3)
>>  
>>  #define GICR_TYPER_CPU_NUMBER(r)	(((r) >> 8) & 0xffff)
>>  
>>
> 
> Thanks,
> 
> 	M.
> 

-- 
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.