linux-kernel - Re: [PATCH] arm64/kernel/entry: refine comment of stack overflow check

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Message-ID: <0aee0354-5153-940c-bf72-7bd6bccce490@huawei.com>
Date:   Tue, 3 Dec 2019 08:55:53 +0800
From:   Guoheyi <guoheyi@...wei.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <wanghaibin.wang@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>
Subject: Re: [PATCH] arm64/kernel/entry: refine comment of stack overflow
 check


在 2019/12/2 20:33, Mark Rutland 写道:
> On Mon, Dec 02, 2019 at 07:37:02PM +0800, Heyi Guo wrote:
>> Stack overflow checking can be done by testing
>> sp & (1 << THREAD_SHIFT)
>> only for the stacks are aligned to (2 << THREAD_SHIFT) with size of
>> (1 << THREAD_SIZE), and this is the case when CONFIG_VMAP_STACK is
>> set.
> Good point, I was sloppy with this comment.
>
>> Fix the code comment to avoid confusion.
>>
>> Signed-off-by: Heyi Guo <guoheyi@...wei.com>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will@...nel.org>
>> ---
>>   arch/arm64/kernel/entry.S | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index cf3bd2976e57..9e8ba507090f 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -76,7 +76,8 @@ alternative_else_nop_endif
>>   #ifdef CONFIG_VMAP_STACK
>>   	/*
>>   	 * Test whether the SP has overflowed, without corrupting a GPR.
>> -	 * Task and IRQ stacks are aligned to (1 << THREAD_SHIFT).
>> +	 * Task and IRQ stacks are aligned to (2 << THREAD_SHIFT) with size of
>> +	 * (1 << THREAD_SHIFT).
>>   	 */
> Can we make that:
>
> 	Task and IRQ stacks are aligned so that SP & (1 << THREAD_SHIFT)
> 	should always be zero.
>
> ... which I think is a bit clearer.

Sure :)

Thanks,

Heyi

>
> With that wording:
>
> Acked-by: Mark Rutland <mark.rutland@....com>
>
> Mark.
>
>>   	add	sp, sp, x0			// sp' = sp + x0
>>   	sub	x0, sp, x0			// x0' = sp' - x0 = (sp + x0) - x0 = sp
>> -- 
>> 2.19.1
>>
> .