[PATCH v3 1/5] x86: Update x86 low level version check of microcode

[Fouad Hilly <fouad.hilly@xxxxxxxxx>]

Update microcode version check at Intel and AMD Level by:
Preventing the low level code from sending errors if the microcode
version is not a newer version. this is required to allow developers to do
ucode loading testing, including the introduction of Intel "min rev" field,
which requires an override mechanism for newer version checks. Even though
the check for newer is removed at this level, it still exists at higher
common level, where by default only newer version will be processed.
The option to override version check, will be added as part of this patch
series.
Other errors will be handled as required at this level.
Keep all the required code at low level that checks for signature and CPU 
compatibility

Signed-off-by: Fouad Hilly <fouad.hilly@xxxxxxxxx>
---
[v3]
1- Update intel code to return errors in case of invalid microcode only.
2- Update code comments.
3- Update commit message and its description

[v2]
Update message description to better describe the changes
 xen/arch/x86/cpu/microcode/amd.c   |  7 +++----
 xen/arch/x86/cpu/microcode/intel.c | 10 ++++------
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 17e68697d5bf..316469ec06e4 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -384,11 +384,10 @@ static struct microcode_patch *cf_check 
cpu_request_microcode(
             }
 
             /*
-             * If the new ucode covers current CPU, compare ucodes and store 
the
-             * one with higher revision.
+             * If the microcode covers current CPU, then store its
+             * revision.
              */
-            if ( (microcode_fits(mc->patch) != MIS_UCODE) &&
-                 (!saved || (compare_header(mc->patch, saved) == NEW_UCODE)) )
+            if ( (microcode_fits(mc->patch) != MIS_UCODE) && !saved )
             {
                 saved = mc->patch;
                 saved_size = mc->len;
diff --git a/xen/arch/x86/cpu/microcode/intel.c 
b/xen/arch/x86/cpu/microcode/intel.c
index 96f34b336b21..de9115974d08 100644
--- a/xen/arch/x86/cpu/microcode/intel.c
+++ b/xen/arch/x86/cpu/microcode/intel.c
@@ -294,8 +294,7 @@ 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;
 
     wbinvd();
@@ -355,11 +354,10 @@ static struct microcode_patch *cf_check 
cpu_request_microcode(
             break;
 
         /*
-         * If the new update covers current CPU, compare updates and store the
-         * one with higher revision.
+         * If the microcode covers current CPU, then store its
+         * revision.
          */
-        if ( (microcode_update_match(mc) != MIS_UCODE) &&
-             (!saved || compare_revisions(saved->rev, mc->rev) == NEW_UCODE) )
+        if ( (microcode_update_match(mc) != MIS_UCODE) && !saved )
             saved = mc;
 
         buf  += blob_size;
-- 
2.42.0