[PATCH v2 1/5] x86: Update x86 low level version check of microcode

[Fouad Hilly]

Update microcode version check at Intel and AMD Level by:
Preventing the low level code from sending errors if the microcode
version provided is not a newer version. Other errors will be sent like before.
When the provided microcode version is the same as the current one, code
to point to microcode provided.
Microcode version check happens at higher and common level in core.c.
Keep all the required code at low level that checks for signature and CPU 
compatibility

[v2]
Update message description to better describe the changes

Signed-off-by: Fouad Hilly <fouad.hi...@cloud.com>
---
 xen/arch/x86/cpu/microcode/amd.c   |  8 ++------
 xen/arch/x86/cpu/microcode/intel.c | 11 +++--------
 2 files changed, 5 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 75fc84e445ce..4f805f662701 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -383,12 +383,8 @@ static struct microcode_patch *cf_check 
cpu_request_microcode(
                 goto skip;
             }
 
-            /*
-             * If the new ucode covers current CPU, compare ucodes and store 
the
-             * one with higher revision.
-             */
-            if ( (microcode_fits(mc->patch) != MIS_UCODE) &&
-                 (!saved || (compare_header(mc->patch, saved) == NEW_UCODE)) )
+            /* If the provided ucode covers current CPU, then store its 
revision. */
+            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 060c529a6e5d..e65c02a57987 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 != NEW_UCODE && result != SAME_UCODE )
         return -EINVAL;
 
     wbinvd();
@@ -354,12 +353,8 @@ static struct microcode_patch *cf_check 
cpu_request_microcode(
         if ( error )
             break;
 
-        /*
-         * If the new update covers current CPU, compare updates and store the
-         * one with higher revision.
-         */
-        if ( (microcode_update_match(mc) != MIS_UCODE) &&
-             (!saved || compare_revisions(saved->rev, mc->rev) == NEW_UCODE) )
+        /* If the provided ucode covers current CPU, then store its revision. 
*/
+        if ( (microcode_update_match(mc) != MIS_UCODE) && !saved )
             saved = mc;
 
         buf  += blob_size;
-- 
2.42.0