[xen stable-4.19] x86/ucode: Fix error handling during parallel ucode load

[patchbot@xxxxxxx]

commit cda5eec07b5dbe2b9be35ace0e3479964344b866
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Nov 25 09:39:49 2025 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Nov 25 09:39:49 2025 +0100

    x86/ucode: Fix error handling during parallel ucode load
    
    The xen-ucode utility is sensitive to the overall error as -EEXIST is a
    special case for success, but the real error can get clobbered with -EBUSY.
    
    This can be demonstrated most easily by force loading an old microcode, 
which
    should yield -EIO but yields -EBUSY:
    
      # xen-ucode /lib/firmware/amd-ucode/microcode_amd_fam17h.bin --force
      Failed to update microcode. (err: Device or resource busy)
    
      (XEN) 256 cores are to update their microcode
      (XEN) microcode: CPU0 update rev 0x830107d to 0x830107c failed, result 
0x830107d
      (XEN) Late loading aborted: CPU0 failed to update ucode: -5
    
    wait_for_state() returns false on encountering LOADING_EXIT.  Right now, 
this
    is always transformed into -EBUSY and passed back to callers.
    
    However, control_thread_fn() can move directly to this state in the case of 
an
    early error; it is not an error condition for APs, but the latest write into
    stopmachine_data.fn_result wins, causing the real error, -EIO, to get
    clobbered with -EBUSY.
    
    Drop all the -EBUSY's, and treat hitting LOADING_EXIT as a success case.  
This
    causes only a single error to be returned through stop_machine_run(), and
    preserves the -EIO
    
      # xen-ucode /lib/firmware/amd-ucode/microcode_amd_fam17h.bin --force
      Failed to update microcode. (err: Input/output error)
    
      (XEN) 256 cores are to update their microcode
      (XEN) microcode: CPU0 update rev 0x830107d to 0x830107c failed, result 
0x830107d
      (XEN) Late loading aborted: CPU0 failed to update ucode: -5
    
    Fixes: 5ed12565aa32 ("microcode: rendezvous CPUs in NMI handler and load 
ucode")
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: a405bf42eddeb2a2e656807882176e37bd2378af
    master date: 2025-11-24 15:17:39 +0000
---
 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 e2d8ab8b24..e38e5eb7ff 100644
--- a/xen/arch/x86/cpu/microcode/core.c
+++ b/xen/arch/x86/cpu/microcode/core.c
@@ -376,7 +376,9 @@ static int secondary_nmi_work(void)
 {
     cpumask_set_cpu(smp_processor_id(), &cpu_callin_map);
 
-    return wait_for_state(LOADING_EXIT) ? 0 : -EBUSY;
+    wait_for_state(LOADING_EXIT);
+
+    return 0;
 }
 
 static int primary_thread_work(const struct microcode_patch *patch)
@@ -386,7 +388,7 @@ static int primary_thread_work(const struct microcode_patch 
*patch)
     cpumask_set_cpu(smp_processor_id(), &cpu_callin_map);
 
     if ( !wait_for_state(LOADING_ENTER) )
-        return -EBUSY;
+        return 0;
 
     ret = alternative_call(ucode_ops.apply_microcode, patch);
     if ( !ret )
@@ -427,7 +429,7 @@ static int cf_check microcode_nmi_callback(
 static int secondary_thread_fn(void)
 {
     if ( !wait_for_state(LOADING_CALLIN) )
-        return -EBUSY;
+        return 0;
 
     self_nmi();
 
@@ -449,7 +451,7 @@ static int secondary_thread_fn(void)
 static int primary_thread_fn(const struct microcode_patch *patch)
 {
     if ( !wait_for_state(LOADING_CALLIN) )
-        return -EBUSY;
+        return 0;
 
     if ( ucode_in_nmi )
     {
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.19