diff --git a/xen/arch/x86/microcode.c b/xen/arch/x86/microcode.c
index 03bc0aa..f0b1e39 100644
--- a/xen/arch/x86/microcode.c
+++ b/xen/arch/x86/microcode.c
@@ -189,12 +189,20 @@ static DEFINE_SPINLOCK(microcode_mutex);
 
 DEFINE_PER_CPU(struct cpu_signature, cpu_sig);
 
-struct microcode_info {
-    unsigned int cpu;
-    uint32_t buffer_size;
-    int error;
-    char buffer[1];
-};
+/*
+ * Return a patch that covers current CPU. If there are multiple patches,
+ * return the one with the highest revision number. Return error If no
+ * patch is found and an error occurs during the parsing process. Otherwise
+ * return NULL.
+ */
+static struct microcode_patch *microcode_parse_blob(const char *buf,
+                                                    uint32_t len)
+{
+    if ( likely(!microcode_ops->collect_cpu_info(&this_cpu(cpu_sig))) )
+        return microcode_ops->cpu_request_microcode(buf, len);
+
+    return NULL;
+}
 
 int microcode_resume_cpu(void)
 {
@@ -220,13 +228,6 @@ void microcode_free_patch(struct microcode_patch *microcode_patch)
     xfree(microcode_patch);
 }
 
-const struct microcode_patch *microcode_get_cache(void)
-{
-    ASSERT(spin_is_locked(&microcode_mutex));
-
-    return microcode_cache;
-}
-
 /* Return true if cache gets updated. Otherwise, return false */
 bool microcode_update_cache(struct microcode_patch *patch)
 {
@@ -250,49 +251,88 @@ bool microcode_update_cache(struct microcode_patch *patch)
     return true;
 }
 
-static int microcode_update_cpu(const void *buf, size_t size)
+/*
+ * Load a microcode update to current CPU.
+ *
+ * If no patch is provided, the cached patch will be loaded. Microcode update
+ * during APs bringup and CPU resuming falls into this case.
+ */
+static int microcode_update_cpu(const struct microcode_patch *patch)
 {
-    int err;
-    unsigned int cpu = smp_processor_id();
-    struct cpu_signature *sig = &per_cpu(cpu_sig, cpu);
+    int err = microcode_ops->collect_cpu_info(&this_cpu(cpu_sig));
+
+    if ( unlikely(err) )
+        return err;
 
     spin_lock(&microcode_mutex);
 
-    err = microcode_ops->collect_cpu_info(sig);
-    if ( likely(!err) )
-        err = microcode_ops->cpu_request_microcode(buf, size);
+    if ( patch )
+    {
+        /*
+         * If a patch is specified, it should has newer revision than
+         * that of the patch cached.
+         */
+        if ( microcode_cache &&
+             microcode_ops->compare_patch(patch, microcode_cache) != NEW_UCODE )
+        {
+            spin_unlock(&microcode_mutex);
+            return -EINVAL;
+        }
+    }
+    else if ( microcode_cache )
+        patch = microcode_cache;
+    else
+        /* No patch to update */
+        err = -ENOENT;
+
+    if ( patch )
+    {
+        err = microcode_ops->apply_microcode(patch);
+        /* clean up patch cache if we failed to load the cached patch */
+        if ( patch == microcode_cache && err == -EIO )
+        {
+            microcode_free_patch(microcode_cache);
+            microcode_cache = NULL;
+        }
+    }
+
     spin_unlock(&microcode_mutex);
 
     return err;
 }
 
-static long do_microcode_update(void *_info)
+static long do_microcode_update(void *patch)
 {
-    struct microcode_info *info = _info;
-    int error;
-
-    BUG_ON(info->cpu != smp_processor_id());
+    unsigned int cpu;
 
-    error = microcode_update_cpu(info->buffer, info->buffer_size);
-    if ( error )
-        info->error = error;
+    /* store the patch after a successful loading */
+    if ( !microcode_update_cpu(patch) && patch )
+    {
+        spin_lock(&microcode_mutex);
+        microcode_update_cache(patch);
+        spin_unlock(&microcode_mutex);
+        patch = NULL;
+    }
 
     if ( microcode_ops->end_update )
         microcode_ops->end_update();
 
-    info->cpu = cpumask_next(info->cpu, &cpu_online_map);
-    if ( info->cpu < nr_cpu_ids )
-        return continue_hypercall_on_cpu(info->cpu, do_microcode_update, info);
+    cpu = cpumask_next(smp_processor_id(), &cpu_online_map);
+    if ( cpu < nr_cpu_ids )
+        return continue_hypercall_on_cpu(cpu, do_microcode_update, patch);
+
+    /* Free the patch if no CPU has loaded it successfully. */
+    if ( patch )
+        microcode_free_patch(patch);
 
-    error = info->error;
-    xfree(info);
-    return error;
+    return 0;
 }
 
 int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
 {
     int ret;
-    struct microcode_info *info;
+    void *buffer;
+    struct microcode_patch *patch;
 
     if ( len != (uint32_t)len )
         return -E2BIG;
@@ -300,32 +340,44 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
     if ( microcode_ops == NULL )
         return -EINVAL;
 
-    info = xmalloc_bytes(sizeof(*info) + len);
-    if ( info == NULL )
+    buffer = xmalloc_bytes(len);
+    if ( !buffer )
         return -ENOMEM;
 
-    ret = copy_from_guest(info->buffer, buf, len);
-    if ( ret != 0 )
+    if ( copy_from_guest(buffer, buf, len) )
     {
-        xfree(info);
-        return ret;
+        ret = -EFAULT;
+        goto free;
     }
 
-    info->buffer_size = len;
-    info->error = 0;
-    info->cpu = cpumask_first(&cpu_online_map);
-
     if ( microcode_ops->start_update )
     {
         ret = microcode_ops->start_update();
         if ( ret != 0 )
-        {
-            xfree(info);
-            return ret;
-        }
+            goto free;
+    }
+
+    patch = microcode_parse_blob(buffer, len);
+    if ( IS_ERR(patch) )
+    {
+        ret = PTR_ERR(patch);
+        printk(XENLOG_INFO "Parsing microcode blob error %d\n", ret);
+        goto free;
     }
 
-    return continue_hypercall_on_cpu(info->cpu, do_microcode_update, info);
+    if ( !patch )
+    {
+        printk(XENLOG_INFO "No ucode found. Update aborted!\n");
+        ret = -EINVAL;
+        goto free;
+    }
+
+    ret = continue_hypercall_on_cpu(cpumask_first(&cpu_online_map),
+                                    do_microcode_update, patch);
+
+ free:
+    xfree(buffer);
+    return ret;
 }
 
 static int __init microcode_init(void)
@@ -372,15 +424,40 @@ int __init early_microcode_update_cpu(bool start_update)
 
     microcode_ops->collect_cpu_info(&this_cpu(cpu_sig));
 
+    if ( !start_update )
+        return microcode_update_cpu(NULL);
+
     if ( data )
     {
-        if ( start_update && microcode_ops->start_update )
+        struct microcode_patch *patch;
+
+        if ( microcode_ops->start_update )
             rc = microcode_ops->start_update();
 
         if ( rc )
             return rc;
 
-        return microcode_update_cpu(data, len);
+        patch = microcode_parse_blob(data, len);
+        if ( IS_ERR(patch) )
+        {
+            printk(XENLOG_INFO "Parsing microcode blob error %ld\n",
+                   PTR_ERR(patch));
+            return PTR_ERR(patch);
+        }
+
+        if ( !patch )
+        {
+            printk(XENLOG_INFO "No ucode found. Update aborted!\n");
+            return -EINVAL;
+        }
+
+        spin_lock(&microcode_mutex);
+        rc = microcode_update_cache(patch);
+        spin_unlock(&microcode_mutex);
+
+        ASSERT(rc);
+
+        return microcode_update_cpu(NULL);
     }
     else
         return -ENOMEM;
diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
index fed044a..93d2a98 100644
--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -446,9 +446,11 @@ static bool_t check_final_patch_levels(unsigned int cpu)
     return 0;
 }
 
-static int cpu_request_microcode(const void *buf, size_t bufsize)
+static struct microcode_patch *cpu_request_microcode(const void *buf,
+                                                     size_t bufsize)
 {
     struct microcode_amd *mc_amd;
+    struct microcode_patch *patch = NULL;
     size_t offset = 0;
     int error = 0;
     unsigned int current_cpu_id;
@@ -553,19 +555,22 @@ static int cpu_request_microcode(const void *buf, size_t bufsize)
             break;
         }
 
-        /* Update cache if this patch covers current CPU */
-        if ( microcode_fits(new_patch->mc_amd) != MIS_UCODE )
-            microcode_update_cache(new_patch);
-        else
-            microcode_free_patch(new_patch);
-
-        if ( match_cpu(microcode_get_cache()) )
+        /*
+         * If the new patch covers current CPU, compare patches and store the
+         * one with higher revision.
+         */
+        if ( (microcode_fits(new_patch->mc_amd) != MIS_UCODE) &&
+             (!patch || (compare_patch(new_patch, patch) == NEW_UCODE)) )
         {
-            error = apply_microcode(microcode_get_cache());
-            if ( error )
-                break;
+            struct microcode_patch *tmp = patch;
+
+            patch = new_patch;
+            new_patch = tmp;
         }
 
+        if ( new_patch )
+            microcode_free_patch(new_patch);
+
         if ( offset >= bufsize )
             break;
 
@@ -599,13 +604,10 @@ static int cpu_request_microcode(const void *buf, size_t bufsize)
     xfree(mc_amd);
 
   out:
-    /*
-     * In some cases we may return an error even if processor's microcode has
-     * been updated. For example, the first patch in a container file is loaded
-     * successfully but subsequent container file processing encounters a
-     * failure.
-     */
-    return error;
+    if ( error && !patch )
+        patch = ERR_PTR(error);
+
+    return patch;
 }
 
 static int start_update(void)
diff --git a/xen/arch/x86/microcode_intel.c b/xen/arch/x86/microcode_intel.c
index bcb48bc..8780be0 100644
--- a/xen/arch/x86/microcode_intel.c
+++ b/xen/arch/x86/microcode_intel.c
@@ -279,15 +279,9 @@ static enum microcode_match_result compare_patch(
                                   old_header->pf, old_header->rev);
 }
 
-/*
- * return 0 - no update found
- * return 1 - found update
- * return < 0 - error
- */
-static int get_matching_microcode(const void *mc)
+static struct microcode_patch *alloc_microcode_patch(
+    const struct microcode_header_intel *mc_header)
 {
-    struct cpu_signature *sig = &this_cpu(cpu_sig);
-    const struct microcode_header_intel *mc_header = mc;
     unsigned long total_size = get_totalsize(mc_header);
     void *new_mc = xmalloc_bytes(total_size);
     struct microcode_patch *new_patch = xmalloc(struct microcode_patch);
@@ -296,26 +290,12 @@ static int get_matching_microcode(const void *mc)
     {
         xfree(new_patch);
         xfree(new_mc);
-        return -ENOMEM;
+        return ERR_PTR(-ENOMEM);
     }
-    memcpy(new_mc, mc, total_size);
+    memcpy(new_mc, mc_header, total_size);
     new_patch->mc_intel = new_mc;
 
-    /* Make sure that this patch covers current CPU */
-    if ( microcode_update_match(&new_patch->mc_intel->hdr, sig->sig,
-                                sig->pf, sig->rev) == MIS_UCODE )
-    {
-        microcode_free_patch(new_patch);
-        return 0;
-    }
-
-    microcode_update_cache(new_patch);
-
-    pr_debug("microcode: CPU%d found a matching microcode update with"
-             " version %#x (current=%#x)\n",
-             smp_processord_id(), mc_header->rev, sig->rev);
-
-    return 1;
+    return new_patch;
 }
 
 static int apply_microcode(const struct microcode_patch *patch)
@@ -391,26 +371,46 @@ static long get_next_ucode_from_buffer(void **mc, const u8 *buf,
     return offset + total_size;
 }
 
-static int cpu_request_microcode(const void *buf, size_t size)
+static struct microcode_patch *cpu_request_microcode(const void *buf,
+                                                     size_t size)
 {
     long offset = 0;
     int error = 0;
     void *mc;
+    struct microcode_patch *patch = NULL;
+    const struct cpu_signature *sig = &this_cpu(cpu_sig);
 
     while ( (offset = get_next_ucode_from_buffer(&mc, buf, size, offset)) > 0 )
     {
+        struct microcode_patch *new_patch;
+
         error = microcode_sanity_check(mc);
         if ( error )
             break;
-        error = get_matching_microcode(mc);
-        if ( error < 0 )
+
+        new_patch = alloc_microcode_patch(mc);
+        if ( IS_ERR(new_patch) )
+        {
+            error = PTR_ERR(new_patch);
             break;
+        }
+
         /*
-         * It's possible the data file has multiple matching ucode,
-         * lets keep searching till the latest version
+         * If the new patch covers current CPU, compare patches and store the
+         * one with higher revision.
          */
-        if ( error == 1 )
-            error = 0;
+        if ( (microcode_update_match(&new_patch->mc_intel->hdr, sig->sig,
+                                     sig->pf, sig->rev) != MIS_UCODE) &&
+             (!patch || (compare_patch(new_patch, patch) == NEW_UCODE)) )
+        {
+            struct microcode_patch *tmp = patch;
+
+            patch = new_patch;
+            new_patch = tmp;
+        }
+
+        if ( new_patch )
+            microcode_free_patch(new_patch);
 
         xfree(mc);
     }
@@ -419,10 +419,10 @@ static int cpu_request_microcode(const void *buf, size_t size)
     if ( offset < 0 )
         error = offset;
 
-    if ( !error && match_cpu(microcode_get_cache()) )
-        error = apply_microcode(microcode_get_cache());
+    if ( error && !patch )
+        patch = ERR_PTR(error);
 
-    return error;
+    return patch;
 }
 
 static const struct microcode_ops microcode_intel_ops = {
diff --git a/xen/include/asm-x86/microcode.h b/xen/include/asm-x86/microcode.h
index 8c7de9d..8e71615 100644
--- a/xen/include/asm-x86/microcode.h
+++ b/xen/include/asm-x86/microcode.h
@@ -20,7 +20,8 @@ struct microcode_patch {
 };
 
 struct microcode_ops {
-    int (*cpu_request_microcode)(const void *buf, size_t size);
+    struct microcode_patch *(*cpu_request_microcode)(const void *buf,
+                                                     size_t size);
     int (*collect_cpu_info)(struct cpu_signature *csig);
     int (*apply_microcode)(const struct microcode_patch *patch);
     int (*start_update)(void);
@@ -41,8 +42,6 @@ struct cpu_signature {
 DECLARE_PER_CPU(struct cpu_signature, cpu_sig);
 extern const struct microcode_ops *microcode_ops;
 
-const struct microcode_patch *microcode_get_cache(void);
-bool microcode_update_cache(struct microcode_patch *patch);
 void microcode_free_patch(struct microcode_patch *patch);
 
 #endif /* ASM_X86__MICROCODE_H */
