[PATCH v5 22/24] mm: use custom page_free for P2PDMA pages

[Logan Gunthorpe]

When P2PDMA pages are passed to userspace, they will need to be
reference counted properly and returned to their genalloc after their
reference count returns to 1. This is accomplished with the existing
DEV_PAGEMAP_OPS and the .page_free() operation.

Change CONFIG_P2PDMA to select CONFIG_DEV_PAGEMAP_OPS and add
MEMORY_DEVICE_PCI_P2PDMA to page_is_devmap_managed(),
devmap_managed_enable_[put|get]() and free_devmap_managed_page().

Signed-off-by: Logan Gunthorpe <logang at deltatee.com>
---
 drivers/pci/p2pdma.c | 13 +++++++++++++
 mm/memremap.c        |  5 +++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index e66694cc9e14..3a24bf5099cf 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -101,6 +101,18 @@ static const struct attribute_group p2pmem_group = {
 	.name = "p2pmem",
 };
 
+static void p2pdma_page_free(struct page *page)
+{
+	struct pci_p2pdma_pagemap *pgmap = to_p2p_pgmap(page->pgmap);
+
+	gen_pool_free(pgmap->provider->p2pdma->pool,
+		      (uintptr_t)page_to_virt(page), PAGE_SIZE);
+}
+
+static const struct dev_pagemap_ops p2pdma_pgmap_ops = {
+	.page_free = p2pdma_page_free,
+};
+
 static void pci_p2pdma_release(void *data)
 {
 	struct pci_dev *pdev = data;
@@ -198,6 +210,7 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
 	pgmap->range.end = pgmap->range.start + size - 1;
 	pgmap->nr_range = 1;
 	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
+	pgmap->ops = &p2pdma_pgmap_ops;
 
 	p2p_pgmap->provider = pdev;
 	p2p_pgmap->bus_offset = pci_bus_address(pdev, bar) -
diff --git a/mm/memremap.c b/mm/memremap.c
index 0fc8b85d792e..ced9448ddcb4 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -299,6 +299,10 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 	case MEMORY_DEVICE_GENERIC:
 		break;
 	case MEMORY_DEVICE_PCI_P2PDMA:
+		if (!pgmap->ops->page_free) {
+			WARN(1, "Missing page_free method\n");
+			return ERR_PTR(-EINVAL);
+		}
 		params.pgprot = pgprot_noncached(params.pgprot);
 		break;
 	default:
@@ -460,6 +464,7 @@ void free_zone_device_page(struct page *page)
 {
 	switch (page->pgmap->type) {
 	case MEMORY_DEVICE_PRIVATE:
+	case MEMORY_DEVICE_PCI_P2PDMA:
 		free_device_page(page);
 		return;
 	case MEMORY_DEVICE_FS_DAX:
-- 
2.30.2