1 files changed, 26 insertions, 2 deletions

diff --git a/arch/x86/include/asm/bios_ebda.h b/arch/x86/include/asm/bios_ebda.h
index 3c7521063d3f..aa6a3170ab5a 100644
--- a/arch/x86/include/asm/bios_ebda.h
+++ b/arch/x86/include/asm/bios_ebda.h
@@ -4,16 +4,40 @@
 #include <asm/io.h>
 
 /*
- * there is a real-mode segmented pointer pointing to the
- * 4K EBDA area at 0x40E.
+ * Returns physical address of EBDA.  Returns 0 if there is no EBDA.
  */
 static inline unsigned int get_bios_ebda(void)
 {
+        /*
+         * There is a real-mode segmented pointer pointing to the
+         * 4K EBDA area at 0x40E.
+         */
         unsigned int address = *(unsigned short *)phys_to_virt(0x40E);
         address <<= 4;
         return address; /* 0 means none */
 }
 
+/*
+ * Return the sanitized length of the EBDA in bytes, if it exists.
+ */
+static inline unsigned int get_bios_ebda_length(void)
+{
+        unsigned int address;
+        unsigned int length;
+
+        address = get_bios_ebda();
+        if (!address)
+                return 0;
+
+        /* EBDA length is byte 0 of the EBDA (stored in KiB) */
+        length = *(unsigned char *)phys_to_virt(address);
+        length <<= 10;
+
+        /* Trim the length if it extends beyond 640KiB */
+        length = min_t(unsigned int, (640 * 1024) - address, length);
+        return length;
+}
+
 void reserve_ebda_region(void);
 
 #ifdef CONFIG_X86_CHECK_BIOS_CORRUPTION