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Message-ID: <8087e009-4eca-ab92-cbca-23ccfb3fafac@codeaurora.org>
Date: Thu, 22 Mar 2018 14:41:09 -0500
From: Shanker Donthineni <shankerd@...eaurora.org>
To: Marc Zyngier <marc.zyngier@....com>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Cc: Mark Rutland <mark.rutland@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Jason Cooper <jason@...edaemon.net>,
Vikram Sethi <vikrams@...eaurora.org>
Subject: Re: [PATCH v3] irqchip/gic-v3: Ensure GICR_CTLR.EnableLPI=0 is
observed before enabling
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@...eaurora.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.
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