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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Message-ID: <bd9acf43-d97b-3a11-bca2-b82f71467d2f@huawei.com>
Date:   Fri, 6 Nov 2020 18:05:36 +0800
From:   "xuqiang (M)" <xuqiang36@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     <tglx@...utronix.de>, <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.


在 2020/11/5 22:24, Marc Zyngier 写道:
> On 2020-11-05 14:06, xuqiang (M) wrote:
>> 在 2020/11/5 21:12, Marc Zyngier 写道:
>>> Please don't top-post.
>>>
>>> On 2020-11-05 11:54, xuqiang (M) wrote:
>>>> 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.
>>>
>>> This cannot work. By doing a memset on the command queue, you are
>>> only feeding crap to the ITS (command 0 simply does not exist).
>>> Consider yourself lucky that it doesn't just lock-up.
>>>
>>> What needs to happen is the restore sequence that is already in the
>>> driver, so that the command queue is in a sane state before re-enabling
>>> the ITS.
>>>
>>>         M.
>>
>>
>> On my platform, ITS_FLAGS_SAVE_SUSPEND_STATE is not set, thus
>> the first if condition in its_save_disable under list_for_each_entry 
>> goes
>> to the continue, however, I want to set the GITS_CWRITER to 0 at the
>> end of list_for_each_entry.
>>
>> Do you have any suggestions about how to do this?
>
> That's pretty much dropping the checks for ITS_FLAGS_SAVE_SUSPEND_STATE,
> isn't it? But I assume your ITS is already enabled by the time you 
> reenter
> the kernel? If so, I bet your firmware is doing more than just writing
> to CBASER and CWRITER...
>
>         M.

Yes, you are right.My firmware stores GITS_CTRL,GITS_CBASER,GITS_CWRITER

and GITS_BASER<n> in the suspend, and restores these registers in the 
resume.

So I will drop the checks for ITS_FLAGS_SAVE_SUSPEND_STATE. In the case 
of ITS disabled,

set the GITS_CWRITER to 0.

Thanks

              Xu.