linux-kernel - [PATCH RFC 01/13] mm/hmm: Process pud swap entry without pud

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Message-ID: <20240306104147.193052-2-peterx@redhat.com>
Date: Wed,  6 Mar 2024 18:41:35 +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,
	Alistair Popple <apopple@...dia.com>
Subject: [PATCH RFC 01/13] mm/hmm: Process pud swap entry without pud_huge()

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

Swap pud entries do not always return true for pud_huge() for all archs.
x86 and sparc (so far) allow it, but all the rest do not accept a swap
entry to be reported as pud_huge().  So it's not safe to check swap entries
within pud_huge().  Check swap entries before pud_huge(), so it should be
always safe.

This is the only place in the kernel that (IMHO, wrongly) relies on
pud_huge() to return true on pud swap entries.  The plan is to cleanup
pXd_huge() to only report non-swap mappings for all archs.

Cc: Alistair Popple <apopple@...dia.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 mm/hmm.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 277ddcab4947..c44391a0246e 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -424,7 +424,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 	walk->action = ACTION_CONTINUE;
 
 	pud = READ_ONCE(*pudp);
-	if (pud_none(pud)) {
+	if (pud_none(pud) || !pud_present(pud)) {
 		spin_unlock(ptl);
 		return hmm_vma_walk_hole(start, end, -1, walk);
 	}
@@ -435,11 +435,6 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 		unsigned long *hmm_pfns;
 		unsigned long cpu_flags;
 
-		if (!pud_present(pud)) {
-			spin_unlock(ptl);
-			return hmm_vma_walk_hole(start, end, -1, walk);
-		}
-
 		i = (addr - range->start) >> PAGE_SHIFT;
 		npages = (end - addr) >> PAGE_SHIFT;
 		hmm_pfns = &range->hmm_pfns[i];
-- 
2.44.0