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

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Date:   Tue, 10 Jan 2023 10:01:53 +0200
From:   Yishai Hadas <yishaih@...dia.com>
To:     Matthew Wilcox <willy@...radead.org>
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 10/01/2023 7:08, Matthew Wilcox wrote:
> 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;

In this area of the patch I just reverted to what we had in 6.1 [1] 
where we were good.

I can send V1 and replace the 'paddr' to be called 'last_pfn' if it's 
really needed.

Alternatively, we can stay with this patch version unless you can see 
here any real issue.

What do you suggest ?

[1] https://elixir.bootlin.com/linux/v6.1.4/source/lib/scatterlist.c#L462

Yishai