[PATCH v4 1/3] xsm: only search for a policy file when needed

["Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>]

It is possible to select a few different build configurations that results in
the unnecessary walking of the boot module list looking for a policy module.
This specifically occurs when the flask policy is enabled but either the dummy
or the SILO policy is selected as the enforcing policy. This is not ideal for
configurations like hyperlaunch and dom0less when there could be a number of
modules to be walked or doing an unnecessary device tree lookup.

This patch introduces the policy_file_required flag for tracking when an XSM
policy module requires a policy file. Only when the policy_file_required flag
is set to true, will XSM search the boot modules for a policy file.

Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/xsm/xsm_core.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/xen/xsm/xsm_core.c b/xen/xsm/xsm_core.c
index 2286a502e3..675e4f552c 100644
--- a/xen/xsm/xsm_core.c
+++ b/xen/xsm/xsm_core.c
@@ -55,19 +55,31 @@ static enum xsm_bootparam __initdata xsm_bootparam =
     XSM_BOOTPARAM_DUMMY;
 #endif
 
+static bool __initdata policy_file_required =
+    IS_ENABLED(CONFIG_XSM_FLASK_DEFAULT);
+
 static int __init cf_check parse_xsm_param(const char *s)
 {
     int rc = 0;
 
     if ( !strcmp(s, "dummy") )
+    {
         xsm_bootparam = XSM_BOOTPARAM_DUMMY;
+        policy_file_required = false;
+    }
 #ifdef CONFIG_XSM_FLASK
     else if ( !strcmp(s, "flask") )
+    {
         xsm_bootparam = XSM_BOOTPARAM_FLASK;
+        policy_file_required = true;
+    }
 #endif
 #ifdef CONFIG_XSM_SILO
     else if ( !strcmp(s, "silo") )
+    {
         xsm_bootparam = XSM_BOOTPARAM_SILO;
+        policy_file_required = false;
+    }
 #endif
     else
         rc = -EINVAL;
@@ -148,7 +160,7 @@ int __init xsm_multiboot_init(
 
     printk("XSM Framework v" XSM_FRAMEWORK_VERSION " initialized\n");
 
-    if ( XSM_MAGIC )
+    if ( policy_file_required )
     {
         ret = xsm_multiboot_policy_init(module_map, mbi, &policy_buffer,
                                         &policy_size);
@@ -176,7 +188,7 @@ int __init xsm_dt_init(void)
 
     printk("XSM Framework v" XSM_FRAMEWORK_VERSION " initialized\n");
 
-    if ( XSM_MAGIC )
+    if ( policy_file_required )
     {
         ret = xsm_dt_policy_init(&policy_buffer, &policy_size);
         if ( ret )
-- 
2.20.1