[PATCH v3 1/5] x86/microcode: Allow reading microcode revision even if it can't be updated

[Alejandro Vallejo <alejandro.vallejo@cloud.com>]

The code currently assumes all microcode handlers are set or none are. That
won't be the case in a future patch, as apply_microcode() may not be set
while the others are. Hence, this patch allows reading the microcode
revision even if updating it is unavailable.

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
---
v3:
  * Hunks taken from v2/patch4 (Jan)
---
 xen/arch/x86/cpu/microcode/core.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/cpu/microcode/core.c b/xen/arch/x86/cpu/microcode/core.c
index e65af4b82e..df7e1df870 100644
--- a/xen/arch/x86/cpu/microcode/core.c
+++ b/xen/arch/x86/cpu/microcode/core.c
@@ -750,11 +750,12 @@ __initcall(microcode_init);
 /* Load a cached update to current cpu */
 int microcode_update_one(void)
 {
+    if ( ucode_ops.collect_cpu_info )
+        alternative_vcall(ucode_ops.collect_cpu_info);
+
     if ( !ucode_ops.apply_microcode )
         return -EOPNOTSUPP;
 
-    alternative_vcall(ucode_ops.collect_cpu_info);
-
     return microcode_update_cpu(NULL);
 }
 
@@ -860,6 +861,9 @@ int __init early_microcode_init(unsigned long *module_map,
         break;
     }
 
+    if ( ucode_ops.collect_cpu_info )
+        ucode_ops.collect_cpu_info();
+
     if ( !ucode_ops.apply_microcode )
     {
         printk(XENLOG_WARNING "Microcode loading not available\n");
@@ -868,8 +872,6 @@ int __init early_microcode_init(unsigned long *module_map,
 
     microcode_grab_module(module_map, mbi);
 
-    ucode_ops.collect_cpu_info();
-
     if ( ucode_mod.mod_end || ucode_blob.size )
         rc = early_microcode_update_cpu();
 
-- 
2.34.1