Re: [PATCH 02/12] pci/p2pdma: Don't initialise page refcount to one

Logan Gunthorpe
2024-09-11T00:50:54Z

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

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

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

Thanks,

Logan