linux-kernel - Re: [PATCH v2 04/32] mm/pgtable: allow pte_offset_map[

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Date:   Sat, 5 Aug 2023 18:07:05 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Yongqin Liu <yongqin.liu@...aro.org>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Yang Shi <shy828301@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Peter Xu <peterx@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Alistair Popple <apopple@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Steven Price <steven.price@....com>,
        SeongJae Park <sj@...nel.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Huang Ying <ying.huang@...el.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Zack Rusin <zackr@...are.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Minchan Kim <minchan@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Song Liu <song@...nel.org>,
        Thomas Hellstrom <thomas.hellstrom@...ux.intel.com>,
        Ryan Roberts <ryan.roberts@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 04/32] mm/pgtable: allow pte_offset_map[_lock]() to
 fail

On Sun, Aug 06, 2023 at 12:06:28AM +0800, Yongqin Liu wrote:
> On Sat, 29 Jul 2023 at 00:58, Hugh Dickins <hughd@...gle.com> wrote:
> >
> > On Fri, 28 Jul 2023, Matthew Wilcox wrote:
> > > On Fri, Jul 28, 2023 at 09:53:29PM +0800, Yongqin Liu wrote:
> > > > Hi, Hugh
> > > >
> > > > It seems this change makes pte_offset_map_lock not possible to be
> > > > called in out of tree modules,
> > > > otherwise it will report error like this:
> > > >         ERROR: modpost: "__pte_offset_map_lock"
> > > > [../omap-modules/android-mainline/pvr/pvrsrvkm.ko] undefined!
> > > >
> > > > Not sure if you have any idea about it, and any suggestions on how to
> > > > resolve it?
> > >
> > > Please explain why this module needs to map page tables
> >
> > +1
> Sorry, I am not able to give any explanation here,
> I am not familiar with the pvrsrvkm source, I just use it to have one
> working AOSP build.
> 
> here is the source file where pte_offset_map_lock is called,
>     https://android-git.linaro.org/kernel/omap-modules.git/tree/pvr/services4/srvkm/env/linux/osfunc.c?h=android-mainline#n3508
> in case you could know something with a quick look.

Isn't this just get_user_pages()?