Not like fault_in_readable() or fault_in_writeable(), in
fault_in_safe_writeable() local variable 'start' is increased page
by page to loop till the whole address range is handled. However,
it mistakenly calcalates the size of handled range with 'uaddr - start'.

Fix it here.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
v1->v2:
- Fix a patch log typo caused by copy-and-paste error. Thanks
  to Yanjun.

 mm/gup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 855ab860f88b..73777b1de679 100644
--- 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);
-- 
2.41.0

On 31.03.25 10:13, Baoquan He wrote:
> Not like fault_in_readable() or fault_in_writeable(), in
> fault_in_safe_writeable() local variable 'start' is increased page
> by page to loop till the whole address range is handled. However,
> it mistakenly calcalates the size of handled range with 'uaddr - start'.
> 
> Fix it here.

Fixes: ? Do we know of user-visible effects?

> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
> v1->v2:
> - Fix a patch log typo caused by copy-and-paste error. Thanks
>    to Yanjun.
> 
>   mm/gup.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 855ab860f88b..73777b1de679 100644
> --- 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.

(maybe we should also handle the types of these variables similar to as 
in fault_in_readable)

-- 
Cheers,

David / dhildenb

On 04/01/25 at 10:10am, David Hildenbrand wrote:
> On 31.03.25 10:13, Baoquan He wrote:
> > Not like fault_in_readable() or fault_in_writeable(), in
> > fault_in_safe_writeable() local variable 'start' is increased page
> > by page to loop till the whole address range is handled. However,
> > it mistakenly calcalates the size of handled range with 'uaddr - start'.
> > 
> > Fix it here.
> 
> Fixes: ? Do we know of user-visible effects?

I believe it should impact, while I didn't hear of any complaint.
Yeah, it's worth to have one Fixes.

> 
> > 
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> > v1->v2:
> > - Fix a patch log typo caused by copy-and-paste error. Thanks
> >    to Yanjun.
> > 
> >   mm/gup.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 855ab860f88b..73777b1de679 100644
> > --- 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.

Sounds good to me, that makes these similar blocks own consistent code
style. Will change in v3. Thanks for reviewing.

> 
> (maybe we should also handle the types of these variables similar to as in
> fault_in_readable)
> 
> -- 
> Cheers,
> 
> David / dhildenb
>

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

On 04/01/25 at 04:00pm, Oscar Salvador wrote:
> 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. 

Will change in v3 as both of you suggested, thanks for reviewing this v2
series.