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

Alistair Popple
2024-10-11T00:23:15Z

Logan Gunthorpe <logang@deltatee.com> writes:

> 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.

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