cxl: Fix number of allocated pages in SPA

commit 4108efb0 upstream.

The scheduled process area is currently allocated before assigning the
correct maximum processes to the AFU, which will mean we only ever
allocate a fixed number of pages for the scheduled process area. This
will limit us to 958 processes with 2 x 64K pages. If we try to use more
processes than that we'd probably overrun the buffer and corrupt memory
or crash.

AFUs that require three or more interrupts per process will not be
affected as they are already limited to less processes than that, but we
could hit it on an AFU that requires 0, 1 or 2 interrupts per process,
or when using 4K pages.

This patch moves the initialisation of the num_procs to before the SPA
allocation so that enough pages will be allocated for the number of
processes that the AFU supports.
Signed-off-by: Christophe Lombard <clombard@linux.vnet.ibm.com>
Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[ kamal: backport to 4.2-stable: context ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/misc/cxl/native.c

@@ -397,6 +397,7 @@ static int activate_afu_directed(struct cxl_afu *afu)
 
 	dev_info(&afu->dev, "Activating AFU directed mode\n");
 
+	afu->num_procs = afu->max_procs_virtualised;
 	if (alloc_spa(afu))
 		return -ENOMEM;
 
@@ -405,7 +406,6 @@ static int activate_afu_directed(struct cxl_afu *afu)
 	cxl_p1n_write(afu, CXL_PSL_ID_An, CXL_PSL_ID_An_F | CXL_PSL_ID_An_L);
 
 	afu->current_mode = CXL_MODE_DIRECTED;
-	afu->num_procs = afu->max_procs_virtualised;
 
 	if ((rc = cxl_chardev_m_afu_add(afu)))
 		return rc;