linux-kernel - Re: mm: delay rmap removal until after TLB flush

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Date:   Wed, 2 Nov 2022 10:55:10 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
        Nick Piggin <npiggin@...il.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Jann Horn <jannh@...gle.com>,
        John Hubbard <jhubbard@...dia.com>, X86 ML <x86@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Joerg Roedel <jroedel@...e.de>,
        Uros Bizjak <ubizjak@...il.com>,
        Alistair Popple <apopple@...dia.com>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: mm: delay rmap removal until after TLB flush

On Wed, Nov 2, 2022 at 2:15 AM Christian Borntraeger
<borntraeger@...ux.ibm.com> wrote:
>
> It certainly needs a build fix for s390:
>
> In file included from kernel/sched/core.c:78:
> ./arch/s390/include/asm/tlb.h: In function '__tlb_remove_page_size':
> ./arch/s390/include/asm/tlb.h:50:17: error: implicit declaration of function 'page_zap_pte_rmap' [-Werror=implicit-function-declaration]
>     50 |                 page_zap_pte_rmap(page);
>        |                 ^~~~~~~~~~~~~~~~~

Hmm. I'm not sure if I can add a

   #include <linux/rmap.h>

to that s390 asm header file without causing more issues.

The minimal damage would probably be to duplicate the declaration of
page_zap_pte_rmap() in the s390 asm/tlb.h header where it is used.

Not pretty to have two different declarations of that thing, but
anything that then includes both <asm/tlb.h> and <linux/rmap.h> (which
is much of mm) would then verify the consistency of  them.

So I'll do that minimal fix and update that branch, but if s390 people
end up having a better fix, please holler.

                Linus