diff -r 848049b14ec7 xen/arch/x86/microcode_amd.c
--- a/xen/arch/x86/microcode_amd.c	Mon Nov 14 20:15:35 2011 +0000
+++ b/xen/arch/x86/microcode_amd.c	Mon Dec 12 14:36:07 2011 +0100
@@ -27,18 +27,10 @@
 #include <asm/processor.h>
 #include <asm/microcode.h>
 
-#define pr_debug(x...) ((void)0)
-
 #define UCODE_MAGIC                0x00414d44
 #define UCODE_EQUIV_CPU_TABLE_TYPE 0x00000000
 #define UCODE_UCODE_TYPE           0x00000001
 
-#define UCODE_MAX_SIZE          (2048)
-#define DEFAULT_UCODE_DATASIZE  (896)
-#define MC_HEADER_SIZE          (sizeof(struct microcode_header_amd))
-#define DEFAULT_UCODE_TOTALSIZE (DEFAULT_UCODE_DATASIZE + MC_HEADER_SIZE)
-#define DWSIZE                  (sizeof(uint32_t))
-
 /* serialize access to the physical write */
 static DEFINE_SPINLOCK(microcode_update_lock);
 
@@ -99,7 +91,7 @@ static int microcode_fits(void *mc, int 
     }
 
     if ( mc_header->patch_id <= uci->cpu_sig.rev )
-        return -EINVAL;
+        return 1;
 
     printk(KERN_DEBUG "microcode: CPU%d found a matching microcode "
            "update with version 0x%x (current=0x%x)\n",
@@ -147,8 +139,8 @@ static int apply_microcode(int cpu)
     return 0;
 }
 
-static int get_next_ucode_from_buffer_amd(void *mc, const void *buf,
-                                         size_t size, unsigned long *offset)
+static int get_next_ucode_from_buffer_amd(void *mc, size_t *mc_size,
+    const void *buf, size_t size, unsigned long *offset)
 {
     size_t total_size;
     const uint8_t *bufp = buf;
@@ -178,7 +170,12 @@ static int get_next_ucode_from_buffer_am
         return -EINVAL;
     }
 
-    memset(mc, 0, UCODE_MAX_SIZE);
+    if (*mc_size < total_size) {
+        xfree(mc);
+        mc = xmalloc_bytes(total_size);
+        *mc_size = total_size;
+    }
+    memset(mc, 0, *mc_size);
     memcpy(mc, (const void *)(&bufp[off + 8]), total_size);
 
     *offset = off + total_size + 8;
@@ -231,11 +228,12 @@ static int install_equiv_cpu_table(const
 static int cpu_request_microcode(int cpu, const void *buf, size_t size)
 {
     const uint32_t *buf_pos;
-    unsigned long offset = 0;
+    size_t offset = 0;
     int error = 0;
     int ret;
     struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu);
     void *mc;
+    size_t mc_size;
 
     /* We should bind the task to the CPU */
     BUG_ON(cpu != raw_smp_processor_id());
@@ -245,7 +243,7 @@ static int cpu_request_microcode(int cpu
     if ( buf_pos[0] != UCODE_MAGIC )
     {
         printk(KERN_ERR "microcode: error! Wrong "
-               "microcode patch file magic\n");
+            "microcode patch file magic\n");
         return -EINVAL;
     }
 
@@ -256,7 +254,8 @@ static int cpu_request_microcode(int cpu
         return -EINVAL;
     }
 
-    mc = xmalloc_bytes(UCODE_MAX_SIZE);
+    mc_size = buf_pos[offset + 1]; /* Size of 1st microcode patch in bytes */
+    mc = xmalloc_bytes(size);
     if ( mc == NULL )
     {
         printk(KERN_ERR "microcode: error! "
@@ -272,7 +271,8 @@ static int cpu_request_microcode(int cpu
      * It's possible the data file has multiple matching ucode,
      * lets keep searching till the latest version
      */
-    while ( (ret = get_next_ucode_from_buffer_amd(mc, buf, size, &offset)) == 0)
+    while ( (ret = get_next_ucode_from_buffer_amd(mc, &mc_size,
+        buf, size, &offset)) == 0)
     {
         error = microcode_fits(mc, cpu);
         if (error <= 0)