1 files changed, 18 insertions, 2 deletions

diff --git a/arch/x86/include/asm/bootparam_utils.h b/arch/x86/include/asm/bootparam_utils.h
index 5b5e9cb774b5..653668d140f9 100644
--- a/arch/x86/include/asm/bootparam_utils.h
+++ b/arch/x86/include/asm/bootparam_utils.h
@@ -14,13 +14,29 @@
  * analysis of kexec-tools; if other broken bootloaders initialize a
  * different set of fields we will need to figure out how to disambiguate.
  *
+ * Note: efi_info is commonly left uninitialized, but that field has a
+ * private magic, so it is better to leave it unchanged.
  */
 static void sanitize_boot_params(struct boot_params *boot_params)
 {
+        /* 
+         * IMPORTANT NOTE TO BOOTLOADER AUTHORS: do not simply clear
+         * this field.  The purpose of this field is to guarantee
+         * compliance with the x86 boot spec located in
+         * Documentation/x86/boot.txt .  That spec says that the
+         * *whole* structure should be cleared, after which only the
+         * portion defined by struct setup_header (boot_params->hdr)
+         * should be copied in.
+         *
+         * If you're having an issue because the sentinel is set, you
+         * need to change the whole structure to be cleared, not this
+         * (or any other) individual field, or you will soon have
+         * problems again.
+         */
         if (boot_params->sentinel) {
-                /*fields in boot_params are not valid, clear them */
+                /* fields in boot_params are left uninitialized, clear them */
                 memset(&boot_params->olpc_ofw_header, 0,
-                       (char *)&boot_params->alt_mem_k -
+                       (char *)&boot_params->efi_info -
                         (char *)&boot_params->olpc_ofw_header);
                 memset(&boot_params->kbd_status, 0,
                        (char *)&boot_params->hdr -