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Date: Mon, 14 Jul 2025 15:43:55 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Klara Modin <klarasmodin@gmail.com>
Cc: Youling Tang <youling.tang@linux.dev>, Matthew Wilcox
 <willy@infradead.org>, Jan Kara <jack@suse.cz>,
 linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org, chizhiling@163.com, Youling Tang
 <tangyouling@kylinos.cn>, Chi Zhiling <chizhiling@kylinos.cn>
Subject: Re: [PATCH] mm/filemap: Align last_index to folio size
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On Tue, 15 Jul 2025 00:34:12 +0200 Klara Modin <klarasmodin@gmail.com> wrote:

> iocb->ki_pos is loff_t (long long) while pgoff_t is unsigned long and
> this overflow seems to happen in practice, resulting in last_index being
> before index.
> 
> The following diff resolves the issue for me:
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 3c071307f40e..d2902be0b845 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2585,8 +2585,8 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
>  	int err = 0;
>  
>  	/* "last_index" is the index of the folio beyond the end of the read */
> -	last_index = round_up(iocb->ki_pos + count, mapping_min_folio_nrbytes(mapping));
> -	last_index >>= PAGE_SHIFT;
> +	last_index = round_up(iocb->ki_pos + count,
> +			mapping_min_folio_nrbytes(mapping)) >> PAGE_SHIFT;
>  retry:
>  	if (fatal_signal_pending(current))
>  		return -EINTR;

Looks good, thanks.  I added your signed-off-by (which I trust is OK?)
and queued this up.