Merge branch 'next' into for-linus

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 3c7521063d3..aa6a3170ab5 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