cxl: Fix NULL dereference in cxl_context_init() on PowerVM guests

Commit f67a6722d650 ("cxl: Workaround PE=0 hardware limitation in
Mellanox CX4") added a "min_pe" field to struct cxl_service_layer_ops,
to allow us to work around a Mellanox CX-4 hardware limitation.

When allocating the PE number in cxl_context_init(), we read from
ctx->afu->adapter->native->sl_ops->min_pe to get the minimum PE number.
Unsurprisingly, in a PowerVM guest ctx->afu->adapter->native is NULL,
and guests don't have a cxl_service_layer_ops struct anywhere.

Move min_pe from struct cxl_service_layer_ops to struct cxl so it's
accessible in both native and PowerVM environments. For the Mellanox
CX-4, set the min_pe value in set_sl_ops().

Fixes: f67a6722d650 ("cxl: Workaround PE=0 hardware limitation in Mellanox CX4")
Reported-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Reviewed-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/context.c

@@ -90,8 +90,7 @@ int cxl_context_init(struct cxl_context *ctx, struct cxl_afu *afu, bool master,
 	 */
 	mutex_lock(&afu->contexts_lock);
 	idr_preload(GFP_KERNEL);
-	i = idr_alloc(&ctx->afu->contexts_idr, ctx,
-		      ctx->afu->adapter->native->sl_ops->min_pe,
+	i = idr_alloc(&ctx->afu->contexts_idr, ctx, ctx->afu->adapter->min_pe,
 		      ctx->afu->num_procs, GFP_NOWAIT);
 	idr_preload_end();
 	mutex_unlock(&afu->contexts_lock);

drivers/misc/cxl/cxl.h

@@ -561,7 +561,6 @@ struct cxl_service_layer_ops {
 	u64 (*timebase_read)(struct cxl *adapter);
 	int capi_mode;
 	bool needs_reset_before_disable;
-	int min_pe;
 };
 
 struct cxl_native {
@@ -603,6 +602,7 @@ struct cxl {
 	struct bin_attribute cxl_attr;
 	int adapter_num;
 	int user_irqs;
+	int min_pe;
 	u64 ps_size;
 	u16 psl_rev;
 	u16 base_image;

drivers/misc/cxl/pci.c

@@ -1521,14 +1521,15 @@ static const struct cxl_service_layer_ops xsl_ops = {
 	.write_timebase_ctrl = write_timebase_ctrl_xsl,
 	.timebase_read = timebase_read_xsl,
 	.capi_mode = OPAL_PHB_CAPI_MODE_DMA,
-	.min_pe = 1, /* Workaround for Mellanox CX4 HW bug */
 };
 
 static void set_sl_ops(struct cxl *adapter, struct pci_dev *dev)
 {
 	if (dev->vendor == PCI_VENDOR_ID_MELLANOX && dev->device == 0x1013) {
+		/* Mellanox CX-4 */
 		dev_info(&adapter->dev, "Device uses an XSL\n");
 		adapter->native->sl_ops = &xsl_ops;
+		adapter->min_pe = 1; /* Workaround for CX-4 hardware bug */
 	} else {
 		dev_info(&adapter->dev, "Device uses a PSL\n");
 		adapter->native->sl_ops = &psl_ops;