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From: Alistair Popple <apopple@nvidia.com>
To: linux-mm@kvack.org
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	Alistair Popple <apopple@nvidia.com>
Subject: [RFC 03/10] pci/p2pdma: Don't initialise page refcount to one
Date: Thu, 11 Apr 2024 10:57:24 +1000
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The reference counts for ZONE_DEVICE private pages should be
initialised by the driver when the page is actually allocated by the
driver allocator, not when they are first created. This is currently
the case for MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_COHERENT pages
but not MEMORY_DEVICE_PCI_P2PDMA pages so fix that up.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 drivers/pci/p2pdma.c | 2 ++
 mm/memremap.c        | 8 ++++----
 mm/mm_init.c         | 4 +++-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index fa7370f..ab7ef18 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -128,6 +128,8 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj,
 		goto out;
 	}
 
+	get_page(virt_to_page(kaddr));
+
 	/*
 	 * vm_insert_page() can sleep, so a reference is taken to mapping
 	 * such that rcu_read_unlock() can be done before inserting the
diff --git a/mm/memremap.c b/mm/memremap.c
index bee8556..99d26ff 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -508,15 +508,15 @@ void free_zone_device_page(struct page *page)
 	page->mapping = NULL;
 	page->pgmap->ops->page_free(page);
 
-	if (page->pgmap->type != MEMORY_DEVICE_PRIVATE &&
-	    page->pgmap->type != MEMORY_DEVICE_COHERENT)
+	if (page->pgmap->type == MEMORY_DEVICE_PRIVATE ||
+	    page->pgmap->type == MEMORY_DEVICE_COHERENT)
+		put_dev_pagemap(page->pgmap);
+	else if (page->pgmap->type != MEMORY_DEVICE_PCI_P2PDMA)
 		/*
 		 * Reset the page count to 1 to prepare for handing out the page
 		 * again.
 		 */
 		set_page_count(page, 1);
-	else
-		put_dev_pagemap(page->pgmap);
 }
 
 void zone_device_page_init(struct page *page)
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 50f2f34..da45abd 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -6,6 +6,7 @@
  * Author Mel Gorman <mel@csn.ul.ie>
  *
  */
+#include "linux/memremap.h"
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/kobject.h>
@@ -1006,7 +1007,8 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
 	 * which will set the page count to 1 when allocating the page.
 	 */
 	if (pgmap->type == MEMORY_DEVICE_PRIVATE ||
-	    pgmap->type == MEMORY_DEVICE_COHERENT)
+	    pgmap->type == MEMORY_DEVICE_COHERENT ||
+	    pgmap->type == MEMORY_DEVICE_PCI_P2PDMA)
 		set_page_count(page, 0);
 }
 
-- 
git-series 0.9.1