linux-kernel - Re: [PATCH 2/4] mm/gup: explicitly define and check internal GUP flags, disallow FOLL

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Date:   Mon, 2 Oct 2023 13:00:23 +0200
From:   David Hildenbrand <david@...hat.com>
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>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 2/4] mm/gup: explicitly define and check internal GUP
 flags, disallow FOLL_TOUCH

On 01.10.23 18:00, Lorenzo Stoakes wrote:
> Rather than open-coding a list of internal GUP flags in
> is_valid_gup_args(), define which ones are internal.
> 
> In addition, we were not explicitly checking to see if the user passed in
> FOLL_TOUCH somehow, this patch fixes that.
> 
> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
> ---
>   mm/gup.c      | 5 ++---
>   mm/internal.h | 3 +++
>   2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 2f8a2d89fde1..b21b33d1787e 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2227,12 +2227,11 @@ static bool is_valid_gup_args(struct page **pages, int *locked,
>   	/*
>   	 * These flags not allowed to be specified externally to the gup
>   	 * interfaces:
> -	 * - FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
> +	 * - FOLL_TOUCH/FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
>   	 * - FOLL_REMOTE is internal only and used on follow_page()
>   	 * - FOLL_UNLOCKABLE is internal only and used if locked is !NULL
>   	 */
> -	if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_TRIED | FOLL_UNLOCKABLE |
> -				      FOLL_REMOTE | FOLL_FAST_ONLY)))
> +	if (WARN_ON_ONCE(gup_flags & INTERNAL_GUP_FLAGS))
>   		return false;
>   
>   	gup_flags |= to_set;
> diff --git a/mm/internal.h b/mm/internal.h
> index 449891ad7fdb..499016c6b01d 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1018,6 +1018,9 @@ enum {
>   	FOLL_UNLOCKABLE = 1 << 21,
>   };
>   
> +#define INTERNAL_GUP_FLAGS (FOLL_TOUCH | FOLL_TRIED | FOLL_REMOTE | FOLL_PIN | \
> +			    FOLL_FAST_ONLY | FOLL_UNLOCKABLE)
> +
>   /*
>    * Indicates for which pages that are write-protected in the page table,
>    * whether GUP has to trigger unsharing via FAULT_FLAG_UNSHARE such that the

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb