[PATCH] x86/ucode: Further fixes to identify "ucode already up to date"

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

When the revision in hardware is newer than anything Xen has to hand,
'microcode_cache' isn't set up.  Then, `xen-ucode` initiates the update
because it doesn't know whether the revisions across the system are symmetric
or not.  This involves the patch getting all the way into the
apply_microcode() hooks before being found to be too old.

This is all a giant mess and needs an overhaul, but in the short term simply
adjust the apply_microcode() to return -EEXIST.

Also, unconditionally print the preexisting microcode revision on boot.  It's
relevant information which is otherwise unavailable if Xen doesn't find new
microcode to use.

Fixes: 648db37a155a ("x86/ucode: Distinguish "ucode already up to date"")
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Fouad Hilly <fouad.hilly@xxxxxxxxx>

Sorry Fouad, but this collides with your `--force` series once again.
Hopefully it might make things fractionally easier.

Background: For 06-55-04 (Skylake server, stepping 4 specifically), there's a
recent production firmware update which has a newer microcode revision than
exists in the Intel public microcode repository.  It's causing a mess in our
automated testing, although it is finding good bugs...
---
 xen/arch/x86/cpu/microcode/amd.c   | 7 +++++--
 xen/arch/x86/cpu/microcode/core.c  | 2 ++
 xen/arch/x86/cpu/microcode/intel.c | 7 +++++--
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 17e68697d5bf..f76a563c8b84 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -222,12 +222,15 @@ static int cf_check apply_microcode(const struct 
microcode_patch *patch)
     uint32_t rev, old_rev = sig->rev;
     enum microcode_match_result result = microcode_fits(patch);
 
+    if ( result == MIS_UCODE )
+        return -EINVAL;
+
     /*
      * Allow application of the same revision to pick up SMT-specific changes
      * even if the revision of the other SMT thread is already up-to-date.
      */
-    if ( result != NEW_UCODE && result != SAME_UCODE )
-        return -EINVAL;
+    if ( result == OLD_UCODE )
+        return -EEXIST;
 
     if ( check_final_patch_levels(sig) )
     {
diff --git a/xen/arch/x86/cpu/microcode/core.c 
b/xen/arch/x86/cpu/microcode/core.c
index 762111838f5f..519798dca4af 100644
--- a/xen/arch/x86/cpu/microcode/core.c
+++ b/xen/arch/x86/cpu/microcode/core.c
@@ -881,6 +881,8 @@ int __init early_microcode_init(unsigned long *module_map,
 
     ucode_ops.collect_cpu_info();
 
+    printk(XENLOG_INFO "Boot microcode revision: 0x%08x\n", 
this_cpu(cpu_sig).rev);
+
     /*
      * Some hypervisors deliberately report a microcode revision of -1 to
      * mean that they will not accept microcode updates.
diff --git a/xen/arch/x86/cpu/microcode/intel.c 
b/xen/arch/x86/cpu/microcode/intel.c
index 96f34b336b21..f505aa1b7888 100644
--- a/xen/arch/x86/cpu/microcode/intel.c
+++ b/xen/arch/x86/cpu/microcode/intel.c
@@ -294,10 +294,13 @@ static int cf_check apply_microcode(const struct 
microcode_patch *patch)
 
     result = microcode_update_match(patch);
 
-    if ( result != NEW_UCODE &&
-         !(opt_ucode_allow_same && result == SAME_UCODE) )
+    if ( result == MIS_UCODE )
         return -EINVAL;
 
+    if ( result == OLD_UCODE ||
+         (result == SAME_UCODE && !opt_ucode_allow_same) )
+        return -EEXIST;
+
     wbinvd();
 
     wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)patch->data);
-- 
2.30.2