From: Michal Hocko <mhocko@kernel.org>
To: zijun_hu <zijun_hu@zoho.com>
Cc: zijun_hu@htc.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
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 16:27:00 +0200 [thread overview]
Message-ID: <20160923142700.GS4478@dhcp22.suse.cz> (raw)
In-Reply-To: <d7408c4e-6fe1-f51c-0388-8636f4761ccd@zoho.com>
On Fri 23-09-16 22:14:40, zijun_hu wrote:
> On 2016/9/23 21:33, Michal Hocko wrote:
> > On Fri 23-09-16 21:00:18, zijun_hu wrote:
> >> 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)
> >
> > just look at how we do that for the mmap...
>
> okay
> i don't familiar with mmap code very well now
mmap basically does addr &= PAGE_MASK (modulo mmap_min_addr) and
len = PAGE_ALIGN(len).
this is [star, end) raher than [start, start+len) but you should get the
point I guess.
--
Michal Hocko
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-09-23 14:27 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-21 4:19 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
2016-09-23 13:33 ` Michal Hocko
2016-09-23 14:14 ` zijun_hu
2016-09-23 14:27 ` Michal Hocko [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160923142700.GS4478@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=iamjoonsoo.kim@lge.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@techsingularity.net \
--cc=mingo@kernel.org \
--cc=rientjes@google.com \
--cc=tj@kernel.org \
--cc=zijun_hu@htc.com \
--cc=zijun_hu@zoho.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox