[xen master] x86/ucode: Exit early from early_update_cache() if loading not available

[patchbot@xxxxxxx]

commit 71226054f28ad98ab214b56a15899e8f62a7bca8
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Jun 1 15:26:02 2023 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Jun 1 20:38:41 2023 +0100

    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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/cpu/microcode/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/arch/x86/cpu/microcode/core.c 
b/xen/arch/x86/cpu/microcode/core.c
index cd456c476f..c1033f3bc2 100644
--- 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);
--
generated by git-patchbot for /home/xen/git/xen.git#master