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

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Message-ID: <20231009221922.GC3952@nvidia.com>
Date:   Mon, 9 Oct 2023 19:19:22 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lorenzo Stoakes <lstoakes@...il.com>
Cc:     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>,
        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>,
        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 Sun, Oct 01, 2023 at 05:00:03PM +0100, 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(-)

Does gup_test still work? It uses FOLL_TOUCH?

Hmm. I guess it was broken for a while anyhow:

/* Just the flags we need, copied from mm.h: */
#define FOLL_WRITE	0x01	/* check pte is writable */
#define FOLL_TOUCH	0x02	/* mark page accessed */

Aside from that this seems OK

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason