linux-kernel - Re: [PATCH] lib/scatterlist: Fix to calculate the last

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Message-ID: <Y7zyyTxdoJulq7OD@casper.infradead.org>
Date:   Tue, 10 Jan 2023 05:08:25 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Yishai Hadas <yishaih@...dia.com>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-mm@...ck.org, jgg@...dia.com, axboe@...nel.dk,
        logang@...tatee.com, hch@....de, alex.williamson@...hat.com,
        leonro@...dia.com, maorg@...dia.com
Subject: Re: [PATCH] lib/scatterlist: Fix to calculate the last_pg properly

On Mon, Jan 09, 2023 at 04:47:01PM +0200, Yishai Hadas wrote:
>  	if (sgt_append->prv) {
> +		unsigned long paddr =
> +			(page_to_pfn(sg_page(sgt_append->prv)) * PAGE_SIZE +

1. page_to_pfn() * PAGE_SIZE is spelled page_to_phys()

2. physical addresses have type phys_addr_t.  Oh, wait, paddr isn't a
physical address, it's a pfn because you divide by PAGE_SIZE at the end.
But you will get truncation on 32-bit, because page_to_pfn() has type
unsigned long.  Anyway, this shouldn't be called paddr.  Maybe last_pfn
or something?

> +			 sgt_append->prv->offset + sgt_append->prv->length) /
> +			PAGE_SIZE;