RDMA/ucontext: Add a core API for mmaping driver IO memory

To support disassociation and PCI hot unplug, we have to track all the
VMAs that refer to the device IO memory. When disassociation occurs the
VMAs have to be revised to point to the zero page, not the IO memory, to
allow the physical HW to be unplugged.

The three drivers supporting this implemented three different versions
of this algorithm, all leaving something to be desired. This new common
implementation has a few differences from the driver versions:

- Track all VMAs, including splitting/truncating/etc. Tie the lifetime of
  the private data allocation to the lifetime of the vma. This avoids any
  tricks with setting vm_ops which Linus didn't like. (see link)
- Support multiple mms, and support properly tracking mmaps triggered by
  processes other than the one first opening the uverbs fd. This makes
  fork behavior of disassociation enabled drivers the same as fork support
  in normal drivers.
- Don't use crazy get_task stuff.
- Simplify the approach for to racing between vm_ops close and
  disassociation, fixing the related bugs most of the driver
  implementations had. Since we are in core code the tracking list can be
  placed in struct ib_uverbs_ufile, which has a lifetime strictly longer
  than any VMAs created by mmap on the uverbs FD.

Link: https://www.spinics.net/lists/stable/msg248747.html
Link: https://lkml.kernel.org/r/CA+55aFxJTV_g46AQPoPXen-UPiqR1HGMZictt7VpC-SMFbm3Cw@mail.gmail.com
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index e463d3007a35..a66238d8a2a3 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -2646,6 +2646,28 @@ void *ib_get_client_data(struct ib_device *device, struct ib_client *client);
 void  ib_set_client_data(struct ib_device *device, struct ib_client *client,
 			 void *data);
 
+#if IS_ENABLED(CONFIG_INFINIBAND_USER_ACCESS)
+int rdma_user_mmap_io(struct ib_ucontext *ucontext, struct vm_area_struct *vma,
+		      unsigned long pfn, unsigned long size, pgprot_t prot);
+int rdma_user_mmap_page(struct ib_ucontext *ucontext,
+			struct vm_area_struct *vma, struct page *page,
+			unsigned long size);
+#else
+static inline int rdma_user_mmap_io(struct ib_ucontext *ucontext,
+				    struct vm_area_struct *vma,
+				    unsigned long pfn, unsigned long size,
+				    pgprot_t prot)
+{
+	return -EINVAL;
+}
+static inline int rdma_user_mmap_page(struct ib_ucontext *ucontext,
+				struct vm_area_struct *vma, struct page *page,
+				unsigned long size)
+{
+	return -EINVAL;
+}
+#endif
+
 static inline int ib_copy_from_udata(void *dest, struct ib_udata *udata, size_t len)
 {
 	return copy_from_user(dest, udata->inbuf, len) ? -EFAULT : 0;