linux-kernel - Re: [PATCH v4 7/7] mm/mm_init: Use for_each_valid_pfn() in init_unavailable

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: <84b46ea0-12a1-469f-921e-2d0fd6dacd0d@redhat.com>
Date: Mon, 28 Apr 2025 09:12:57 +0200
From: David Hildenbrand <david@...hat.com>
To: David Woodhouse <dwmw2@...radead.org>, Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 "Sauerwein, David" <dssauerw@...zon.de>,
 Anshuman Khandual <anshuman.khandual@....com>,
 Ard Biesheuvel <ardb@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
 Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Mike Rapoport <rppt@...ux.ibm.com>, Will Deacon <will@...nel.org>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, Ruihan Li <lrh2000@....edu.cn>
Subject: Re: [PATCH v4 7/7] mm/mm_init: Use for_each_valid_pfn() in
 init_unavailable_range()

On 26.04.25 01:04, David Woodhouse wrote:
> On Fri, 2025-04-25 at 22:12 +0200, David Hildenbrand wrote:
>>
>> In any case, trying to figure out why Lorenzo ran into an issue ... if
>> it's nit because of the pageblock, maybe something in for_each_valid_pfn
>> with sparsemem is still shaky.
> 
> Yep, I think this was it:
> 
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -2190,10 +2190,10 @@ static inline unsigned long next_valid_pfn(unsigned long pfn, unsigned long end_
>          /*
>           * Either every PFN within the section (or subsection for VMEMMAP) is
>           * valid, or none of them are. So there's no point repeating the check
> -        * for every PFN; only call first_valid_pfn() the first time, and when
> -        * crossing a (sub)section boundary (i.e. !(pfn & ~PFN_VALID_MASK)).
> +        * for every PFN; only call first_valid_pfn() again when crossing a
> +        * (sub)section boundary (i.e. !(pfn & ~PAGE_{SUB,}SECTION_MASK)).
>           */
> -       if (pfn & (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) ?
> +       if (pfn & ~(IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) ?
>                     PAGE_SUBSECTION_MASK : PAGE_SECTION_MASK))


LGTM, although we could make way this easier to understand:

Something like:


unsigned long pfn_mask = PAGE_SECTION_MASK;

if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP)
	pfn_mask = PAGE_SUBSECTION_MASK;

if (pfn & ~pfn_mask)
	...

-- 
Cheers,

David / dhildenb