linux-kernel - [PATCH v5 19/25] proc/task_mmu: Mark devdax and fsdax pages as always unpinned

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Message-ID: <e17a04cf8feaa838e62d0c7d1de97444222b7956.1736221254.git-series.apopple@nvidia.com>
Date: Tue,  7 Jan 2025 14:42:35 +1100
From: Alistair Popple <apopple@...dia.com>
To: akpm@...ux-foundation.org,
	dan.j.williams@...el.com,
	linux-mm@...ck.org
Cc: Alistair Popple <apopple@...dia.com>,
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Subject: [PATCH v5 19/25] proc/task_mmu: Mark devdax and fsdax pages as always unpinned

The procfs mmu files such as smaps and pagemap currently ignore devdax and
fsdax pages because these pages are considered special. A future change
will start treating these as normal pages, meaning they can be exposed via
smaps and pagemap.

The only difference is that devdax and fsdax pages can never be pinned for
DMA via FOLL_LONGTERM, so add an explicit check in pte_is_pinned() to
reflect that.

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

---

Changes for v5:

 - After discussion with David remove the checks for DAX pages for
   smaps and pagemap walkers. This means DAX pages will now appear in
   those procfs files.
---
 fs/proc/task_mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 38a5a3e..9a8a7d3 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1378,7 +1378,7 @@ static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr,
 	if (likely(!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags)))
 		return false;
 	folio = vm_normal_folio(vma, addr, pte);
-	if (!folio)
+	if (!folio || folio_is_devdax(folio) || folio_is_fsdax(folio))
 		return false;
 	return folio_maybe_dma_pinned(folio);
 }
-- 
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