linux-kernel - Re: [PATCH -next] irq-chip/gic-v3-its: Fixed an issue where the ITS executes the residual commands in the queue again when the ITS wakes up from sleep mode.

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Date:   Thu, 5 Nov 2020 19:54:50 +0800
From:   "xuqiang (M)" <xuqiang36@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     <tglx@...utronix.de>, <jason@...edaemon.net>,
        <linux-kernel@...r.kernel.org>, <rui.xiang@...wei.com>
Subject: Re: [PATCH -next] irq-chip/gic-v3-its: Fixed an issue where the ITS
 executes the residual commands in the queue again when the ITS wakes up from
 sleep mode.

The kernel sends three commands in the following sequence:

1.mapd(deviceA, ITT_addr1, valid:1)

2.mapti(deviceA):ITS write ITT_addr1 memory;

3.mapd(deviceA, ITT_addr1, valid:0) and kfree(ITT_addr1);

4.mapd(deviceA, ITT_addr2, valid:1);

5.mapti(deviceA):ITS write ITT_addr2 memory;

In this case, the processor enters the sleep mode. After the kernel 
performs the suspend operation, the firmware performs the store 
operation and saves GITS_CBASER and GITS_CWRITER registers.

Then, the processor is woken up, and the firmware restores GITS_CBASER 
and GITS_CWRITER registers. Because GITS_CWRITER register is not 0, ITS 
will read the above command sequence execution from the command queue, 
causing ITT_addr1 memory to be trampled.

Thanks,

                 Xu


在 2020/11/4 2:19, Marc Zyngier 写道:
> On Tue, 03 Nov 2020 08:11:23 +0000,
> Xu Qiang <xuqiang36@...wei.com> wrote:
>> During wakeup, the ATF restore interface restores the values of
>> the cbaser and cwriter registers. As a result, the ITS executes
>> the residual commands in the queue, which may cause memory corruption.
>>
>> To solve this problem, clear all data in the command queue
>> in the suspend interface of the ITS driver.
>>
>> Signed-off-by: Xu Qiang <xuqiang36@...wei.com>
>> ---
>>   drivers/irqchip/irq-gic-v3-its.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 0fec31931e11..b8487f78ac21 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -4741,6 +4741,14 @@ static int its_save_disable(void)
>>   	list_for_each_entry(its, &its_nodes, entry) {
>>   		void __iomem *base;
>>   
>> +		/*
>> +		 * Clear the command queue so that the ITS will not re-execute
>> +		 * the remaining commands in the command queue when
>> +		 * the cwriter and cbaser registers are restored
>> +		 * in the restore interface of the firmware.
>> +		 */
>> +		memset(its->cmd_base, 0, ITS_CMD_QUEUE_SZ);
>> +
>>   		if (!(its->flags & ITS_FLAGS_SAVE_SUSPEND_STATE))
>>   			continue;
> You are wiping the ITS queue before even stopping the ITS. How well is
> that going to work? What if there is something in flight?
>
> I don't understand what you are trying to do here, nor how ATF is
> involved. So please describe the whole sequence of events, and we'll
> decide whether that's something we need to fix.
>
> Thanks,
>
> 	M.
>