linux-kernel - [PATCH RFC 03/13] mm/gup: Check p4d presence before going on

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Date: Wed,  6 Mar 2024 18:41:37 +0800
From: peterx@...hat.com
To: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: linuxppc-dev@...ts.ozlabs.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Muchun Song <muchun.song@...ux.dev>,
	Jason Gunthorpe <jgg@...dia.com>,
	peterx@...hat.com,
	Matthew Wilcox <willy@...radead.org>,
	Mike Rapoport <rppt@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	x86@...nel.org,
	sparclinux@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: [PATCH RFC 03/13] mm/gup: Check p4d presence before going on

From: Peter Xu <peterx@...hat.com>

Currently there should have no p4d swap entries so it may not matter much,
however this may help us to rule out swap entries in pXd_huge() API, which
will include p4d_huge().  The p4d_present() checks make it 100% clear that
we won't rely on p4d_huge() for swap entries.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 mm/gup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 69a777f4fc5c..f87a7d90f2ae 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -776,7 +776,7 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,
 
 	p4dp = p4d_offset(pgdp, address);
 	p4d = READ_ONCE(*p4dp);
-	if (p4d_none(p4d))
+	if (p4d_none(p4d) || !p4d_present(p4d))
 		return no_page_table(vma, flags);
 	BUILD_BUG_ON(p4d_huge(p4d));
 	if (unlikely(p4d_bad(p4d)))
@@ -3069,7 +3069,7 @@ static int gup_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, unsigned lo
 		p4d_t p4d = READ_ONCE(*p4dp);
 
 		next = p4d_addr_end(addr, end);
-		if (p4d_none(p4d))
+		if (p4d_none(p4d) || !p4d_present(p4d))
 			return 0;
 		BUILD_BUG_ON(p4d_huge(p4d));
 		if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) {
-- 
2.44.0