Re: [PATCH v2 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier

[Baoquan He <bhe@redhat.com>]

On 04/01/25 at 10:02am, David Hildenbrand wrote:
> On 31.03.25 10:13, Baoquan He wrote:
> > In __get_user_pages(), it will traverse page table and take a reference
> > to the page the given user address corresponds to if GUP_GET or GUP_PIN
> > is et. However, it's not supported both GUP_GET and GUP_PIN are set.
> > This check should be done earlier, but not doing it till entering into
> > follow_page_pte() and failed.
> > 
> > Here move the checking to the beginning of __get_user_pages().
> > 
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> > v1->v2:
> > - Fix code bug caused by copy-and-paste error, this is reported by
> >    lkp test robot.
> > 
> >   mm/gup.c | 10 +++++-----
> >   1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 73777b1de679..f9bce14ed3cd 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -847,11 +847,6 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
> >   	pte_t *ptep, pte;
> >   	int ret;
> > -	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> > -	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
> > -			 (FOLL_PIN | FOLL_GET)))
> > -		return ERR_PTR(-EINVAL);
> > -
> >   	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
> >   	if (!ptep)
> >   		return no_page_table(vma, flags, address);
> > @@ -1434,6 +1429,11 @@ static long __get_user_pages(struct mm_struct *mm,
> >   	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
> > +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> > +	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
> > +			 (FOLL_PIN | FOLL_GET)))
> > +		return -EINVAL;
> > +
> 
> We already have that check in is_valid_gup_args(), that catches all external
> users that could possibly mess this up.

Right.

> 
> So we can just convert that into a VM_WARN_ON_ONCE(), and while doing that,
> we should convert the VM_BUG_ON() above to a VM_WARN_ON_ONCE() as well.

Sounds great to me, will put below change into this patch of v3 as suggested.
Thanks.

diff --git a/mm/gup.c b/mm/gup.c
index 9e4ed09c578b..d551da9549b1 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1427,10 +1427,10 @@ static long __get_user_pages(struct mm_struct *mm,
 
 	start = untagged_addr_remote(mm, start);
 
-	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
+	VM_WARN_ON_ONCE(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
 
 	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
-	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
+	if (VM_WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
 			 (FOLL_PIN | FOLL_GET)))
 		return -EINVAL;