linux-kernel - Re: [PATCH v2 1/7] mm/gup: fix wrongly calculated returned value in fault_in_safe

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Message-ID: <Z-vxZQn3VAQoiRp3@localhost.localdomain>
Date: Tue, 1 Apr 2025 16:00:05 +0200
From: Oscar Salvador <osalvador@...e.de>
To: David Hildenbrand <david@...hat.com>
Cc: Baoquan He <bhe@...hat.com>, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	yanjun.zhu@...ux.dev
Subject: Re: [PATCH v2 1/7] mm/gup: fix wrongly calculated returned value in
 fault_in_safe_writeable()

On Tue, Apr 01, 2025 at 10:10:03AM +0200, David Hildenbrand wrote:
> On 31.03.25 10:13, Baoquan He wrote:
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -2207,8 +2207,8 @@ size_t fault_in_safe_writeable(const char __user *uaddr, size_t size)
> >   	} while (start != end);
> >   	mmap_read_unlock(mm);
> > -	if (size > (unsigned long)uaddr - start)
> > -		return size - ((unsigned long)uaddr - start);
> > +	if (size > start - (unsigned long)uaddr)
> > +		return size - (start - (unsigned long)uaddr);
> >   	return 0;
> >   }
> >   EXPORT_SYMBOL(fault_in_safe_writeable);
> 
> Can we instead just use the uaddr and start variables like in
> fault_in_readable?
> 
> That is, turn "start" into a const and adjust uaddr instead.

Yes, I think that would be much cleaner.

Otherwise, this looks good to me. 

-- 
Oscar Salvador
SUSE Labs