x86/ucode: Exit early from early_update_cache() if loading not available

If for any reason early_microcode_init() concludes that no microcode loading
is available, early_update_cache() will fall over a NULL function pointer:

  (XEN) Xen call trace:
  (XEN)    [<ffff82d04037372e>] R show_code+0x91/0x18f
  (XEN)    [<ffff82d040373a49>] F show_execution_state+0x2d/0x1fc
  (XEN)    [<ffff82d040374210>] F fatal_trap+0x87/0x19a
  (XEN)    [<ffff82d040647f2c>] F init_idt_traps+0/0x1bd
  (XEN)    [<ffff82d04063854f>] F early_page_fault+0x8f/0x94
  (XEN)    [<0000000000000000>] F 0000000000000000
  (XEN)    [<ffff82d040628c46>] F arch/x86/cpu/microcode/core.c#early_update_cache+0x11/0x74
  (XEN)    [<ffff82d040628e5c>] F microcode_init_cache+0x5a/0x5c
  (XEN)    [<ffff82d04064388f>] F __start_xen+0x1e11/0x27ee
  (XEN)    [<ffff82d040206184>] F __high_start+0x94/0xa0

which is actually parse_blob()'s use of ucode_ops.collect_cpu_info.

Skip trying to cache anything if microcode loading is unavailable.

Fixes: dc380df12acf ("x86/ucode: load microcode earlier on boot CPU")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/cpu/microcode/core.c b/xen/arch/x86/cpu/microcode/core.c
index cd456c476fbf066224584d80c001eecc0e8f53d2..c1033f3bc23eeb557e5818ac74e0c73a530557fc 100644 (file)
--- a/xen/arch/x86/cpu/microcode/core.c
+++ b/xen/arch/x86/cpu/microcode/core.c
@@ -789,6 +789,9 @@ int __init microcode_init_cache(unsigned long *module_map,
 {
     int rc = 0;
 
+    if ( !ucode_ops.apply_microcode )
+        return -ENODEV;
+
     if ( ucode_scan )
         /* Need to rescan the modules because they might have been relocated */
         microcode_scan_module(module_map, mbi);