linux-kernel - Re: [PATCH 0/4] various improvements to the GUP interface

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Message-Id: <fdb95a6d-8b54-475c-90c3-8a391161bb66@app.fastmail.com>
Date:   Sun, 01 Oct 2023 13:39:33 -0400
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Lorenzo Stoakes" <lstoakes@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Arnaldo Carvalho de Melo" <acme@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>
Cc:     "Alexander Shishkin" <alexander.shishkin@...ux.intel.com>,
        "Jiri Olsa" <jolsa@...nel.org>,
        "Namhyung Kim" <namhyung@...nel.org>,
        "Ian Rogers" <irogers@...gle.com>,
        "Adrian Hunter" <adrian.hunter@...el.com>,
        "Oleg Nesterov" <oleg@...hat.com>,
        "Richard Cochran" <richardcochran@...il.com>,
        "Jason Gunthorpe" <jgg@...dia.com>,
        "John Hubbard" <jhubbard@...dia.com>
Subject: Re: [PATCH 0/4] various improvements to the GUP interface

On Sun, Oct 1, 2023, at 12:00, Lorenzo Stoakes wrote:
> A series of fixes to simplify and improve the GUP interface with an eye to
> providing groundwork to future improvements:-
>
> * __access_remote_vm() and access_remote_vm() are functionally identical,
>   so make the former static such that in future we can potentially change
>   the external-facing implementation details of this function.
>
> * Extend is_valid_gup_args() to cover the missing FOLL_TOUCH case, and
>   simplify things by defining INTERNAL_GUP_FLAGS to check against.
>
> * Adjust __get_user_pages_locked() to explicitly treat a failure to pin any
>   pages as an error in all circumstances other than FOLL_NOWAIT being
>   specified, bringing it in line with the nommu implementation of this
>   function.
>
> * (With many thanks to Arnd who suggested this in the first instance)
>   Update get_user_page_vma_remote() to explicitly only return a page or an
>   error, simplifying the interface and avoiding the questionable
>   IS_ERR_OR_NULL() pattern.
>
> Lorenzo Stoakes (4):
>   mm: make __access_remote_vm() static
>   mm/gup: explicitly define and check internal GUP flags, disallow
>     FOLL_TOUCH
>   mm/gup: make failure to pin an error if FOLL_NOWAIT not specified
>   mm/gup: adapt get_user_page_vma_remote() to never return NULL

I don't normally review mm patches, but I had a look since it was
started by my earlier feedback. It all looks good to me, very nice
cleanup!

Reviewed-by: Arnd Bergmann <arnd@...db.de>