linux-kernel - Re: [PATCH v2 2/2] mm: fix boundary judgment issues in kernel/resource.c

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Date:   Mon, 21 Jun 2021 14:12:49 +0800
From:   Yaohui Wang <yaohuiwang@...ux.alibaba.com>
To:     Thomas Gleixner <tglx@...utronix.de>, dave.hansen@...ux.intel.com
Cc:     luto@...nel.org, peterz@...radead.org, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, linux-kernel@...r.kernel.org,
        Ben Luo <luoben@...ux.alibaba.com>,
        yaohuiwang@...ux.alibaba.com
Subject: Re: [PATCH v2 2/2] mm: fix boundary judgment issues in
 kernel/resource.c

Hi, Thomas

Thanks for your detailed reply, and your patience for a kernel newbie.

I'll carefully address the formal issues in the next version of patch.


Thanks,

         Yaohui

On 2021/6/20 06:16, Thomas Gleixner wrote:
> Yaohui!
> 
> On Fri, Jun 11 2021 at 12:21, Yaohui Wang wrote:
> 
> The same formal issues as with patch #1
> 
>> The original boundary judgment may ignore @end if @end equals @start. For
> 
> May means it can but it must not. But this is not the case here. end
> equals start is always ignored.
> 
> Also 'original' is meaningless here. Before the patch is applied the
> code is that way.
> 
>   find_next_iomem_res() and __walk_iomem_res_desc() require that the
>   provided end address is larger than the start address, which ...
> 
> 
>> example, if we call ioremap(phys, 1), then @end == @start, and the memory
>> check will not be applied on the page where @end lives, which is
>> unexpected.
> 
> Please avoid 'we' and 'I':
> 
>   is incorrect when ioremap() is invoked with length=1.
> 
>> In kernel/resource.c:find_next_iomem_res, the mem region is a closed
> 
> See the reply to #1 vs. function names. Also please write out 'memory',
> there is no shortage of space in change logs.
> 
>> interval (i.e. [@start..@end]). So @start == @end should be allowed.
> 
> closed interval reads strange. The usual terminology is: The end address
> is inclusive.
> 
>    Resources are described with the start address and the inclusive end
>    address, which means for a resource with 1 byte length the start
>    address is the same as the end address.
> 
>    find_next_iomem_res() and __walk_iomem_res_desc() ignore resources
>    with 1 byte length, which prevents that ioremap(phys, 1) is checked
>    whether it touches non ioremappable resources.
> 
>    ...
> 
> Thanks,
> 
>          tglx
>