linux-kernel - Re: [PATCH v4 1/3] mm: pagewalk: simplify hugepage boundary

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251224092332.53214-1-ioworker0@gmail.com>
Date: Wed, 24 Dec 2025 17:23:32 +0800
From: Lance Yang <ioworker0@...il.com>
To: baolin.wang@...ux.alibaba.com
Cc: Liam.Howlett@...cle.com,
	akpm@...ux-foundation.org,
	axelrasmussen@...gle.com,
	chandna.sahil@...il.com,
	chengming.zhou@...ux.dev,
	david.laight.linux@...il.com,
	david@...nel.org,
	david@...hat.com,
	hannes@...xchg.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	lorenzo.stoakes@...cle.com,
	mhocko@...e.com,
	nphamcs@...il.com,
	rppt@...nel.org,
	shakeel.butt@...ux.dev,
	surenb@...gle.com,
	vbabka@...e.cz,
	weixugc@...gle.com,
	willy@...radead.org,
	yosry.ahmed@...ux.dev,
	yuanchu@...gle.com,
	zhengqi.arch@...edance.com,
	Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH v4 1/3] mm: pagewalk: simplify hugepage boundary

From: Lance Yang <lance.yang@...ux.dev>


On Wed, 24 Dec 2025 15:50:34 +0800, Baolin Wang wrote:
> Hi Andrew,
> 
> On 2025/11/28 15:01, Sahil Chandna wrote:
> > Replace hugepage boundary computation with ALIGN() helper instead of
> > an open coded expression. This helps to improves code readability.
> > 
> > This was flagged by Coccinelle (misc/minmax.cocci) as an opportunity
> > to use min(), after which the boundary computation was updated following
> > review suggestions.
> > 
> > Found by: make coccicheck MODE=report M=mm/
> > No functional change intended.
> > 
> > Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>
> > Suggested-by: David Hildenbrand (Red Hat) <david@...nel.org>
> > Suggested-by: Matthew Wilcox <willy@...radead.org>
> > Suggested-by: David Laight <david.laight.linux@...il.com>
> > Signed-off-by: Sahil Chandna <chandna.sahil@...il.com>
> > ---
> >   mm/pagewalk.c | 3 +--
> >   1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> > index 9f91cf85a5be..9fd59d517f37 100644
> > --- a/mm/pagewalk.c
> > +++ b/mm/pagewalk.c
> > @@ -312,8 +312,7 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
> >   static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
> >   				       unsigned long end)
> >   {
> > -	unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
> > -	return boundary < end ? boundary : end;
> > +	return min(ALIGN(addr, huge_page_size(h)), end);
> >   }
> 
> Please drop this patch from the mm-new branch, as it causes 
> 'run_vmtests.sh' to hang. Specifically, it leads to the system hanging 
> when executing hugepage-vmemmap test, because the program falls into an 
> infinite loop in walk_hugetlb_range() and cannot break out.

Good catch! The problem is that ALIGN() returns addr itself when already
aligned, causing the infinite loop ...

> 
> This patch does introduce functional changes and makes an incorrect 
> assumption that the 'end' must be aligned to the hugepage size. However, 

Yep. This patch is not equivalent to the original code when addr is
already aligned :)

> this is not necessarily the case. For example, see how pagemap_read() 
> calculates the 'end':
> 
> "
> end = start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT);
> "
> 
> Revert this patch, mm selftests work well.