cxl: fix leak of ctx->mapping when releasing kernel API contexts

When a context is created via the kernel API, ctx->mapping is allocated
within the kernel and thus needs to be freed when the context is freed.
reclaim_ctx() attempts to do this for contexts with the ctx->kernelapi flag
set, but afu_release() (which can be called from the kernel API through
cxl_fd_release()) sets ctx->mapping to NULL before calling
cxl_context_free() to free the context.

Add a check to afu_release() so that the mappings in contexts created via
the kernel API are left alone so reclaim_ctx() can free them.

Reported-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Fixes: 6f7f0b3 ("cxl: Add AFU virtual PHB and kernel API")
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Reviewed-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/file.c

@@ -120,9 +120,16 @@ int afu_release(struct inode *inode, struct file *file)
 		 __func__, ctx->pe);
 	cxl_context_detach(ctx);
 
-	mutex_lock(&ctx->mapping_lock);
-	ctx->mapping = NULL;
-	mutex_unlock(&ctx->mapping_lock);
+
+	/*
+	 * Delete the context's mapping pointer, unless it's created by the
+	 * kernel API, in which case leave it so it can be freed by reclaim_ctx()
+	 */
+	if (!ctx->kernelapi) {
+		mutex_lock(&ctx->mapping_lock);
+		ctx->mapping = NULL;
+		mutex_unlock(&ctx->mapping_lock);
+	}
 
 	put_device(&ctx->afu->dev);