linux-kernel - [PATCH v2 06/14] mm/huge_memory: Remove pXd_devmap usage from insert_pXd

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Message-ID: <67bc382c49ed8b165cfbd927886372272c35f508.1750075065.git-series.apopple@nvidia.com>
Date: Mon, 16 Jun 2025 21:58:08 +1000
From: Alistair Popple <apopple@...dia.com>
To: akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	Alistair Popple <apopple@...dia.com>,
	gerald.schaefer@...ux.ibm.com,
	dan.j.williams@...el.com,
	jgg@...pe.ca,
	willy@...radead.org,
	david@...hat.com,
	linux-kernel@...r.kernel.org,
	nvdimm@...ts.linux.dev,
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	John@...ves.net,
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Subject: [PATCH v2 06/14] mm/huge_memory: Remove pXd_devmap usage from insert_pXd_pfn()

Nothing uses PFN_DEV anymore so no need to create devmap pXd's when
mapping a PFN. Instead special mappings will be created which ensures
vm_normal_page_pXd() will not return pages which don't have an
associated page. This could change behaviour slightly on architectures
where pXd_devmap() does not imply pXd_special() as the normal page
checks would have fallen through to checking VM_PFNMAP/MIXEDMAP instead,
which in theory at least could have returned a page.

However vm_normal_page_pXd() should never have been returning pages for
pXd_devmap() entries anyway, so anything relying on that would have been
a bug.

Signed-off-by: Alistair Popple <apopple@...dia.com>

---

Changes since v1:

 - New for v2
---
 mm/huge_memory.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b096240..6514e25 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1415,11 +1415,7 @@ static int insert_pmd(struct vm_area_struct *vma, unsigned long addr,
 		add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
 	} else {
 		entry = pmd_mkhuge(pfn_t_pmd(fop.pfn, prot));
-
-		if (pfn_t_devmap(fop.pfn))
-			entry = pmd_mkdevmap(entry);
-		else
-			entry = pmd_mkspecial(entry);
+		entry = pmd_mkspecial(entry);
 	}
 	if (write) {
 		entry = pmd_mkyoung(pmd_mkdirty(entry));
@@ -1565,11 +1561,7 @@ static void insert_pud(struct vm_area_struct *vma, unsigned long addr,
 		add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PUD_NR);
 	} else {
 		entry = pud_mkhuge(pfn_t_pud(fop.pfn, prot));
-
-		if (pfn_t_devmap(fop.pfn))
-			entry = pud_mkdevmap(entry);
-		else
-			entry = pud_mkspecial(entry);
+		entry = pud_mkspecial(entry);
 	}
 	if (write) {
 		entry = pud_mkyoung(pud_mkdirty(entry));
-- 
git-series 0.9.1