linux-kernel - Re: [PATCH] riscv: fix race when vmap stack overflow

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Message-ID: <ed7c4027-8e15-245f-cdda-0551063761e7@huawei.com>
Date:   Fri, 21 Oct 2022 20:08:36 +0800
From:   Tong Tiangen <tongtiangen@...wei.com>
To:     Andrea Parri <parri.andrea@...il.com>, Guo Ren <guoren@...nel.org>
CC:     Jisheng Zhang <jszhang@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: fix race when vmap stack overflow


在 2022/10/21 16:36, Andrea Parri 写道:
>>>> +     atomic_set_release(&spin_shadow_stack, 0);
>>>
>>> Have not really looked the details: should there be a matching acquire?
>>
>> I use atomic_set_release here, because I need earlier memory
>> operations finished to make sure the sp is ready then set the spin
>> flag.
>>
>> The following memory operations order is not important, because we
>> just care about sp value.
>>
>> Also, we use relax amoswap before, because sp has naturelly
>> dependency. But giving them RCsc is okay here, because we don't care
>> about performance here.
> 
> Thanks for the clarification.
> 
> I'm not really suggesting to add unneeded synchronization, even more
> so in local/private constructs as in this case.  It just felt odd to
> see the release without a pairing acquire, so I asked.  ;-)
> 
> Thanks,
>    Andrea
> 
> 
>> eg:
>>   handle_kernel_stack_overflow:
>> +1:     la sp, spin_shadow_stack
>> +       amoswap.w.aqrl sp, sp, (sp)
>> +       bnez sp, 1b
>> +
>> ....
>> +     smp_store_release(&spin_shadow_stack, 0);
>> +     smp_mb();
> 

Hi Andrea, Zhang, Guo:
	Consider this implementation:)

	smp_store_mb(&spin_shadow_stack, 0);

Thanks,
Tong.
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
> 
> .

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