[v4,2/4] x86/microcode: Ignore microcode loading interface for revision = -1

Commit Message

Alejandro Vallejo June 22, 2023, 5:42 p.m. UTC

Some hypervisors report ~0 as the microcode revision to mean "don't issue
microcode updates". Ignore the microcode loading interface in that case.

Signed-off-by: Alejandro Vallejo <[e-mail]>
Reviewed-by: Jan Beulich <[e-mail]>
---
v4:
  * Stop piggybacking on the existing early exit
---
 xen/arch/x86/cpu/microcode/core.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

Comments

Jan Beulich June 23, 2023, 7:27 a.m. UTC | #1

On 22.06.2023 19:42, Alejandro Vallejo wrote:
> --- a/xen/arch/x86/cpu/microcode/core.c
> +++ b/xen/arch/x86/cpu/microcode/core.c
> @@ -867,10 +867,21 @@ int __init early_microcode_init(unsigned long *module_map,
>          return -ENODEV;
>      }
>  
> -    microcode_grab_module(module_map, mbi);
> -
>      ucode_ops.collect_cpu_info();
>  
> +    /*
> +     * Some hypervisors deliberately report a microcode revision of -1 to
> +     * mean that they will not accept microcode updates. We take the hint
> +     * and ignore the microcode interface in that case.
> +     */
> +    if ( this_cpu(cpu_sig).rev == ~0 ) {

Nit: Style (brace placement). Can probably be fixed up while
committing, if no other issues arise.

Jan

Patch

diff --git a/xen/arch/x86/cpu/microcode/core.c b/xen/arch/x86/cpu/microcode/core.c
index bec8b55db2..e67d143c97 100644
--- a/xen/arch/x86/cpu/microcode/core.c
+++ b/xen/arch/x86/cpu/microcode/core.c
@@ -867,10 +867,21 @@  int __init early_microcode_init(unsigned long *module_map,
         return -ENODEV;
     }
 
-    microcode_grab_module(module_map, mbi);
-
     ucode_ops.collect_cpu_info();
 
+    /*
+     * Some hypervisors deliberately report a microcode revision of -1 to
+     * mean that they will not accept microcode updates. We take the hint
+     * and ignore the microcode interface in that case.
+     */
+    if ( this_cpu(cpu_sig).rev == ~0 ) {
+        printk(XENLOG_WARNING "Microcode loading disabled\n");
+        ucode_ops.apply_microcode = NULL;
+        return -ENODEV;
+    }
+
+    microcode_grab_module(module_map, mbi);
+
     if ( ucode_mod.mod_end || ucode_blob.size )
         rc = early_microcode_update_cpu();