linux-kernel - Re: [PATCH v2] mm/gup: fix gup_fast with dynamic page table folding

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Message-ID: <your-ad-here.call-01600189767-ext-4442@work.hours>
Date:   Tue, 15 Sep 2020 19:09:27 +0200
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>
Cc:     Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Mike Rapoport <rppt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        linux-x86 <x86@...nel.org>,
        linux-arm <linux-arm-kernel@...ts.infradead.org>,
        linux-power <linuxppc-dev@...ts.ozlabs.org>,
        linux-sparc <sparclinux@...r.kernel.org>,
        linux-um <linux-um@...ts.infradead.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Subject: Re: [PATCH v2] mm/gup: fix gup_fast with dynamic page table folding

On Fri, Sep 11, 2020 at 10:36:43PM +0200, Vasily Gorbik wrote:
> Currently to make sure that every page table entry is read just once
> gup_fast walks perform READ_ONCE and pass pXd value down to the next
> gup_pXd_range function by value e.g.:
...snip...
> ---
> v2: added brackets &pgd -> &(pgd)
> 
>  arch/s390/include/asm/pgtable.h | 42 +++++++++++++++++++++++----------
>  include/linux/pgtable.h         | 10 ++++++++
>  mm/gup.c                        | 18 +++++++-------
>  3 files changed, 49 insertions(+), 21 deletions(-)

Andrew, any chance you would pick this up?

There is an Ack from Linus. And I haven't seen any objections from Jason or John.
This seems to be as safe for other architectures as possible.

@Jason and John
Any acks/nacks?

Thank you,
Vasily