From: zijun_hu <zijun_hu@zoho.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
zijun_hu@htc.com, Andrew Morton <akpm@linux-foundation.org>,
tj@kernel.org, mingo@kernel.org, rientjes@google.com,
iamjoonsoo.kim@lge.com, mgorman@techsingularity.net
Subject: Re: [PATCH 1/1] lib/ioremap.c: avoid endless loop under ioremapping page unaligned ranges
Date: Fri, 23 Sep 2016 21:00:18 +0800 [thread overview]
Message-ID: <57E52762.9000702@zoho.com> (raw)
In-Reply-To: <20160923124244.GN4478@dhcp22.suse.cz>
On 09/23/2016 08:42 PM, Michal Hocko wrote:
>>>> no, it don't work for many special case
>>>> for example, provided PMD_SIZE=2M
>>>> mapping [0x1f8800, 0x208800) virtual range will be split to two ranges
>>>> [0x1f8800, 0x200000) and [0x200000,0x208800) and map them separately
>>>> the first range will cause dead loop
>>>
>>> I am not sure I see your point. How can we deadlock if _both_ addresses
>>> get aligned to the page boundary and how does PMD_SIZE make any
>>> difference.
>>>
>> i will take a example to illustrate my considerations
>> provided PUD_SIZE == 1G, PMD_SIZE == 2M, PAGE_SIZE == 4K
>> it is used by arm64 normally
>>
>> we want to map virtual range [0xffffffff_ffc08800, 0xffffffff_fffff800) by
>> ioremap_page_range(),ioremap_pmd_range() is called to map the range
>> finally, ioremap_pmd_range() will call
>> ioremap_pte_range(pmd, 0xffffffff_ffc08800, 0xffffffff_fffe0000) and
>> ioremap_pte_range(pmd, 0xffffffff_fffe0000, 0xffffffff fffff800) separately
>
> but those ranges are not aligned and it ioremap_page_range fix them up
> to _be_ aligned then there is no problem, right? So either I am missing
> something or we are talking past each other.
>
my complementary considerations are show below
why not to round up the range start boundary to page aligned?
1, it don't remain consistent with the original logic
take map [0x1800, 0x4800) as example
the original logic map range [0x1000, 0x2000), but rounding up start boundary
don't mapping the range [0x1000, 0x2000)
2, the rounding up start boundary maybe cause overflow, consider start boundary =
0xffffffff_fffff800
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next prev parent reply other threads:[~2016-09-23 13:00 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-21 4:19 [PATCH 1/1] lib/ioremap.c: avoid endless loop under ioremapping page unaligned ranges zijun_hu
2016-09-22 12:47 ` Michal Hocko
2016-09-22 15:13 ` zijun_hu
2016-09-23 8:45 ` Michal Hocko
2016-09-23 12:29 ` zijun_hu
2016-09-23 12:42 ` Michal Hocko
2016-09-23 13:00 ` zijun_hu [this message]
2016-09-23 13:33 ` Michal Hocko
2016-09-23 14:14 ` zijun_hu
2016-09-23 14:27 ` Michal Hocko
2016-09-23 14:58 ` zijun_hu
2016-09-23 5:53 ` [PATCH v2 " zijun_hu
2016-09-23 14:42 ` [PATCH " Tejun Heo
2016-09-23 15:41 ` zijun_hu
2016-09-23 16:23 ` Tejun Heo
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