[PATCHv4 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path

[Pingfan Liu]

FOLL_LONGTERM suggests a pin which is going to be given to hardware and
can't move. It would truncate CMA permanently and should be excluded.

FOLL_LONGTERM has already been checked in the slow path, but not checked in
the fast path, which means a possible leak of CMA page to longterm pinned
requirement through this crack.

Place a check in gup_pte_range() in the fast path.

Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Keith Busch <keith.busch@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 mm/gup.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 766ae54..de1b03f 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1757,6 +1757,14 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 		page = pte_page(pte);
 
+		/*
+		 * FOLL_LONGTERM suggests a pin given to hardware. Prevent it
+		 * from truncating CMA area
+		 */
+		if (unlikely(flags & FOLL_LONGTERM) &&
+			is_migrate_cma_page(page))
+			goto pte_unmap;
+
 		head = try_get_compound_head(page, 1);
 		if (!head)
 			goto pte_unmap;
@@ -1900,6 +1908,12 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 		refs++;
 	} while (addr += PAGE_SIZE, addr != end);
 
+	if (unlikely(flags & FOLL_LONGTERM) &&
+		is_migrate_cma_page(page)) {
+		*nr -= refs;
+		return 0;
+	}
+
 	head = try_get_compound_head(pmd_page(orig), refs);
 	if (!head) {
 		*nr -= refs;
@@ -1941,6 +1955,12 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 		refs++;
 	} while (addr += PAGE_SIZE, addr != end);
 
+	if (unlikely(flags & FOLL_LONGTERM) &&
+		is_migrate_cma_page(page)) {
+		*nr -= refs;
+		return 0;
+	}
+
 	head = try_get_compound_head(pud_page(orig), refs);
 	if (!head) {
 		*nr -= refs;
@@ -1978,6 +1998,12 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
 		refs++;
 	} while (addr += PAGE_SIZE, addr != end);
 
+	if (unlikely(flags & FOLL_LONGTERM) &&
+		is_migrate_cma_page(page)) {
+		*nr -= refs;
+		return 0;
+	}
+
 	head = try_get_compound_head(pgd_page(orig), refs);
 	if (!head) {
 		*nr -= refs;
-- 
2.7.5