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, 05 Nov 2020 14:24:58 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     "xuqiang (M)" <xuqiang36@...wei.com>
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.

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