diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index ac93df0..f2e8cc9 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -89,12 +89,12 @@ multiboot2_header_start:
                    0, /* Number of the lines - no preference. */ \
                    0  /* Number of bits per pixel - no preference. */
 
-        /* Inhibit bootloader from calling ExitBootServices(). */
+        /* Request that ExitBootServices() not be called. */
         mb2ht_init MB2_HT(EFI_BS), MB2_HT(OPTIONAL)
 
         /* EFI64 entry point. */
         mb2ht_init MB2_HT(ENTRY_ADDRESS_EFI64), MB2_HT(OPTIONAL), \
-                   sym_phys(__efi64_start)
+                   sym_phys(__mb2_efi64_start)
 
         /* Multiboot2 header end tag. */
         mb2ht_init MB2_HT(END), MB2_HT(REQUIRED)
@@ -169,7 +169,7 @@ not_multiboot:
 
         .code64
 
-__efi64_start:
+__mb2_efi64_start:
         cld
 
         /* VGA is not available on EFI platforms. */
@@ -519,6 +519,7 @@ trampoline_setup:
 1:
         /* Switch to low-memory stack.  */
         mov     sym_phys(trampoline_phys),%edi
+        /* The stack ends 64kb after the location of trampoline_phys */
         lea     0x10000(%edi),%esp
         lea     trampoline_boot_cpu_entry-trampoline_start(%edi),%eax
         pushl   $BOOT_CS32
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index dc857d8..d2ebf21 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -146,8 +146,6 @@ static void __init efi_arch_process_memory_map(EFI_SYSTEM_TABLE *SystemTable,
 {
     struct e820entry *e;
     unsigned int i;
-    /* Check for extra mem for mbi data if Xen is loaded via multiboot2 protocol. */
-    UINTN extra_mem = efi_enabled(EFI_LOADER) ? 0 : (64 << 10);
 
     /* Populate E820 table and check trampoline area availability. */
     e = e820map - 1;
@@ -170,8 +168,7 @@ static void __init efi_arch_process_memory_map(EFI_SYSTEM_TABLE *SystemTable,
             /* fall through */
         case EfiConventionalMemory:
             if ( !trampoline_phys && desc->PhysicalStart + len <= 0x100000 &&
-                 len >= cfg.size + extra_mem &&
-                 desc->PhysicalStart + len > cfg.addr )
+                 len >= cfg.size && desc->PhysicalStart + len > cfg.addr )
                 cfg.addr = (desc->PhysicalStart + len - cfg.size) & PAGE_MASK;
             /* fall through */
         case EfiLoaderCode:
@@ -686,6 +683,9 @@ paddr_t __init efi_multiboot2(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTa
     setup_efi_pci();
     efi_variables();
 
+    /* This is the maximum size of our trampoline + our low memory stack */
+    cfg.size = KB(64);
+
     if ( gop )
         efi_set_gop_mode(gop, gop_mode);
 
diff --git a/xen/arch/x86/efi/stub.c b/xen/arch/x86/efi/stub.c
index 6ea6aa1..b81adc0 100644
--- a/xen/arch/x86/efi/stub.c
+++ b/xen/arch/x86/efi/stub.c
@@ -33,7 +33,7 @@ paddr_t __init noreturn efi_multiboot2(EFI_HANDLE ImageHandle,
      * not be directly supported by C compiler.
      */
     asm volatile(
-    "    call %2                      \n"
+    "    call *%2                     \n"
     "0:  hlt                          \n"
     "    jmp  0b                      \n"
        : "+c" (StdErr), "+d" (err) : "g" (StdErr->OutputString)
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index e0e2529..025760f 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -333,3 +333,11 @@ ASSERT(IS_ALIGNED(trampoline_start, 4), "trampoline_start misaligned")
 ASSERT(IS_ALIGNED(trampoline_end,   4), "trampoline_end misaligned")
 ASSERT(IS_ALIGNED(__bss_start,      8), "__bss_start misaligned")
 ASSERT(IS_ALIGNED(__bss_end,        8), "__bss_end misaligned")
+
+/*
+ * The trampolines and the low memory stack must fit in 64kb. In testing
+ * the low memory stack never exceeded 1kb so just require that the
+ * trampolines fit in 63kb, leaving 1kb for the stack.
+ */
+ASSERT((trampoline_end - trampoline_start) < KB(63),
+    "not enough room for trampolines and low memory stack")
diff --git a/xen/include/xen/config.h b/xen/include/xen/config.h
index 473c5e8..04e4da5 100644
--- a/xen/include/xen/config.h
+++ b/xen/include/xen/config.h
@@ -70,6 +70,7 @@
 #define __force
 #define __bitwise
 
+#define KB(_kb)     (_AC(_kb, ULL) << 10)
 #define MB(_mb)     (_AC(_mb, ULL) << 20)
 #define GB(_gb)     (_AC(_gb, ULL) << 30)
 
