tools/arm: Fix nr_spis handling v2

We are missing a way to detect whether a user provided a value for
nr_spis equal to 0 or did not provide any value (default is also 0) which
can cause issues when calculated nr_spis is > 0 and the value from domain
config is 0. Fix it by setting default value for nr_spis to newly added
LIBXL_NR_SPIS_DEFAULT i.e. UINT32_MAX (max supported nr of SPIs is 960
anyway).

Fixes: 55d62b8d46 ("tools/arm: Reject configuration with incorrect nr_spis value")
Reported-by: Luca Fancellu <luca.fancellu@arm.com>
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

tools/include/libxl.h

@@ -1579,6 +1579,7 @@ bool libxl_defbool_val(libxl_defbool db);
 
 const char *libxl_defbool_to_string(libxl_defbool b);
 
+#define LIBXL_NR_SPIS_DEFAULT (~(uint32_t)0)
 #define LIBXL_TIMER_MODE_DEFAULT -1
 #define LIBXL_MEMKB_DEFAULT ~0ULL
 

tools/libs/light/libxl_arm.c

@@ -84,7 +84,7 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
                                       libxl_domain_config *d_config,
                                       struct xen_domctl_createdomain *config)
 {
-    uint32_t nr_spis = 0;
+    uint32_t nr_spis = 0, cfg_nr_spis = d_config->b_info.arch_arm.nr_spis;
     unsigned int i;
     uint32_t vuart_irq, virtio_irq = 0;
     bool vuart_enabled = false, virtio_enabled = false;
@@ -181,13 +181,18 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
 
     LOG(DEBUG, "Configure the domain");
 
-    if (nr_spis > d_config->b_info.arch_arm.nr_spis) {
-        LOG(ERROR, "Provided nr_spis value is too small (minimum required %u)\n",
-            nr_spis);
-        return ERROR_FAIL;
+    /* Check if a user provided a value or not */
+    if (cfg_nr_spis != LIBXL_NR_SPIS_DEFAULT) {
+        if (nr_spis > cfg_nr_spis) {
+            LOG(ERROR, "Provided nr_spis value is too small (minimum required %u)\n",
+                nr_spis);
+            return ERROR_FAIL;
+        }
+        config->arch.nr_spis = cfg_nr_spis;
+    } else {
+        config->arch.nr_spis = nr_spis;
     }
 
-    config->arch.nr_spis = max(nr_spis, d_config->b_info.arch_arm.nr_spis);
     LOG(DEBUG, " - Allocate %u SPIs", config->arch.nr_spis);
 
     switch (d_config->b_info.arch_arm.gic_version) {

tools/libs/light/libxl_types.idl

@@ -723,7 +723,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
     ("arch_arm", Struct(None, [("gic_version", libxl_gic_version),
                                ("vuart", libxl_vuart_type),
                                ("sve_vl", libxl_sve_type),
-                               ("nr_spis", uint32),
+                               ("nr_spis", uint32, {'init_val': 'LIBXL_NR_SPIS_DEFAULT'}),
                               ])),
     ("arch_x86", Struct(None, [("msr_relaxed", libxl_defbool),
                               ])),