linux-kernel - Re: [PATCH 2/4] mm/gup: clean up follow_pfn

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Date:   Mon, 31 Jan 2022 09:36:49 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>, Jan Kara <jack@...e.cz>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/4] mm/gup: clean up follow_pfn_pte() slightly

On Sun, Jan 30, 2022 at 09:17:50PM -0800, John Hubbard wrote:
> Regardless of any FOLL_* flags, get_user_pages() and its variants should
> handle PFN-only entries by stopping early, if the caller expected
> **pages to be filled in.
> 
> This makes for a more reliable API, as compared to the previous approach
> of skipping over such entries (and thus leaving them silently
> unwritten).
> 
> Cc: Peter Xu <peterx@...hat.com>
> Suggested-by: Jason Gunthorpe <jgg@...pe.ca>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---
>  mm/gup.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)

I still think it should be squashed into the previous path, but
otherwise

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

Jason