Logan Gunthorpe [off-list ref] writes:

On 2024-09-09 22:14, Alistair Popple wrote:

quoted

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 |  6 ++++++
 mm/memremap.c        | 17 +++++++++++++----
 mm/mm_init.c         | 22 ++++++++++++++++++----
 3 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 4f47a13..210b9f4 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c

@@ -129,6 +129,12 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj,
 	}
 
 	/*
+	 * Initialise the refcount for the freshly allocated page. As we have
+	 * just allocated the page no one else should be using it.
+	 */
+	set_page_count(virt_to_page(kaddr), 1);
+
+	/*
 	 * vm_insert_page() can sleep, so a reference is taken to mapping
 	 * such that rcu_read_unlock() can be done before inserting the
 	 * pages

This seems to only set reference count to the first page, when there can
be more than one page referenced by kaddr.

Good point.

I suspect the page count adjustment should be done in the for loop
that's a few lines lower than this.

Have moved it there for the next version, thanks!

I think a similar mistake was made by other recent changes.

Thanks,

Logan