linux-kernel - [PATCH v7 17/20] mm/gup: Don't allow FOLL

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Message-ID: <76dec7814edcc56d29be711b2cd344fc98cc66e4.1738709036.git-series.apopple@nvidia.com>
Date: Wed,  5 Feb 2025 09:48:14 +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>,
	Alison Schofield <alison.schofield@...el.com>,
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Subject: [PATCH v7 17/20] mm/gup: Don't allow FOLL_LONGTERM pinning of FS DAX pages

Longterm pinning of FS DAX pages should already be disallowed by
various pXX_devmap checks. However a future change will cause these
checks to be invalid for FS DAX pages so make
folio_is_longterm_pinnable() return false for FS DAX pages.

Signed-off-by: Alistair Popple <apopple@...dia.com>
Reviewed-by: John Hubbard <jhubbard@...dia.com>
Reviewed-by: Dan Williams <dan.j.williams@...el.com>
Acked-by: David Hildenbrand <david@...hat.com>
---
 include/linux/memremap.h | 11 +++++++++++
 include/linux/mm.h       |  7 +++++++
 2 files changed, 18 insertions(+)

diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 0256a42..4aa1519 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -187,6 +187,17 @@ static inline bool folio_is_device_coherent(const struct folio *folio)
 	return is_device_coherent_page(&folio->page);
 }
 
+static inline bool is_fsdax_page(const struct page *page)
+{
+	return is_zone_device_page(page) &&
+		page_pgmap(page)->type == MEMORY_DEVICE_FS_DAX;
+}
+
+static inline bool folio_is_fsdax(const struct folio *folio)
+{
+	return is_fsdax_page(&folio->page);
+}
+
 #ifdef CONFIG_ZONE_DEVICE
 void zone_device_page_init(struct page *page);
 void *memremap_pages(struct dev_pagemap *pgmap, int nid);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6567ece..05a44ae 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2015,6 +2015,13 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
 	if (folio_is_device_coherent(folio))
 		return false;
 
+	/*
+	 * Filesystems can only tolerate transient delays to truncate and
+	 * hole-punch operations
+	 */
+	if (folio_is_fsdax(folio))
+		return false;
+
 	/* Otherwise, non-movable zone folios can be pinned. */
 	return !folio_is_zone_movable(folio);
 
-- 
git-series 0.9.1