On 2020-11-06 10:42 a.m., Jason Gunthorpe wrote:

On Fri, Nov 06, 2020 at 10:28:00AM -0700, Logan Gunthorpe wrote:

quoted

On 2020-11-06 10:22 a.m., Jason Gunthorpe wrote:

quoted

On Fri, Nov 06, 2020 at 10:00:35AM -0700, Logan Gunthorpe wrote:

quoted

Introduce pci_mmap_p2pmem() which is a helper to allocate and mmap
a hunk of p2pmem into userspace.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
 drivers/pci/p2pdma.c       | 104 +++++++++++++++++++++++++++++++++++++
 include/linux/pci-p2pdma.h |   6 +++
 2 files changed, 110 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 9961e779f430..8eab53ac59ae 100644
+++ b/drivers/pci/p2pdma.c

@@ -16,6 +16,7 @@
 #include <linux/genalloc.h>
 #include <linux/memremap.h>
 #include <linux/percpu-refcount.h>
+#include <linux/pfn_t.h>
 #include <linux/random.h>
 #include <linux/seq_buf.h>
 #include <linux/xarray.h>

@@ -1055,3 +1056,106 @@ ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
 	return sprintf(page, "%s\n", pci_name(p2p_dev));
 }
 EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show);
+
+struct pci_p2pdma_map {
+	struct kref ref;
+	struct pci_dev *pdev;
+	void *kaddr;
+	size_t len;
+};

Why have this at all? Nothing uses it and no vm_operations ops are
implemented?

It's necessary to free the allocated p2pmem when the mapping is torn down.

That's suspicious.. Once in a VMA the lifetime of the page must be
controlled by the page refcount, it can't be put back into the genpool
just because the vma was destroed.

Ah, hmm, yes. I guess the pages have to be hooked and returned to the
genalloc through free_devmap_managed_page(). Seems like it might be
doable... but it will complicate things for users that don't want to use
the genpool (though no such users exist upstream).

Logan