Re: [PATCH] mm, hugetlb: correct bit shift in hstate_sizelog

[Andrew Morton]

On Wed, 22 Oct 2014 09:42:46 +0400 Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> wrote:

> On 10/21/2014 10:15 PM, Sasha Levin wrote:
> > hstate_sizelog() would shift left an int rather than long, triggering
> > undefined behaviour and passing an incorrect value when the requested
> > page size was more than 4GB, thus breaking >4GB pages.
> 
> > 
> > Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
> > ---
> >  include/linux/hugetlb.h |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index 65e12a2..57e0dfd 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -312,7 +312,8 @@ static inline struct hstate *hstate_sizelog(int page_size_log)
> >  {
> >  	if (!page_size_log)
> >  		return &default_hstate;
> > -	return size_to_hstate(1 << page_size_log);
> > +
> > +	return size_to_hstate(1UL << page_size_log);
> 
> That still could be undefined on 32-bits. Either use 1ULL or reduce SHM_HUGE_MASK on 32bits.
> 

But

struct hstate *size_to_hstate(unsigned long size)

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