linux-kernel - Re: [RFC PATCH] lib/ioremap: Avoid triggering BUG_ON when end is not PAGE

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Date:   Sat, 31 Mar 2018 09:27:24 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     "Kani, Toshi" <toshi.kani@....com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "guohanjun@...wei.com" <guohanjun@...wei.com>,
        "tanxiaojun@...wei.com" <tanxiaojun@...wei.com>,
        "wangzhou1@...ilicon.com" <wangzhou1@...ilicon.com>,
        "kstewart@...uxfoundation.org" <kstewart@...uxfoundation.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>, "jcm@...hat.com" <jcm@...hat.com>
Subject: Re: [RFC PATCH] lib/ioremap: Avoid triggering BUG_ON when end is not
 PAGE_ALIGN

Hi Toshi,

On 2018/3/31 1:41, Kani, Toshi wrote:
> On Fri, 2018-03-30 at 12:49 +0800, Yisheng Xie wrote:
>> Zhou reported a bug on Hisilicon arm64 D06 platform with 64KB page size:
>  :
>> The cause is the size of PCI IO resource is 32KB, which is 4K aligned but
>> not 64KB aligned, so when do ioremap_pte_range(), its incoming end is not
>> PAGE_ALIGN on 64KB page size system, but ioremap_pte_range increase the
>> addr by PAGE_SIZE, which makes addr != end until trigger BUG_ON.
>>
>> This patch introduces pte_addr_end(addr, end) to resolve this problem, just
>> as what pmd_addr_end do. When end is not PAGE_ALIGN, it will return end
>> instead of addr + PAGE_SIZE, therefore ioremap_pte_range() can break out
>> when real end is coming.
> 
> ioremap_pte_range() assumes that addr and end are aligned by PAGE_SIZE. 
> While some improvement can be made in the range check and documentation,
>  I do not think it is safe for letting this library function to map
> outside of a requested range blindly.
> 
> Can you change the caller of ioremap_page_range() to align the request
> by PAGE_SIZE so that the caller is aware of what it's asking for? 

Sure, as the name of ioremap_*page*_range(), the caller should make sure align
the request by PAGE_SIZE.

Thanks
Yisheng
> 
> Thanks,
> -Toshi
>