From: H. Peter Anvin <hpa@zytor.com>
Date: Wed, 1 Apr 2009 18:35:00 +0000 (-0700)
Subject: x86, setup: guard against pre-ACPI 3 e820 code not updating %ecx
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=cd670599b7b00d9263f6f11a05c0edeb9cbedaf3;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git

x86, setup: guard against pre-ACPI 3 e820 code not updating %ecx

Impact: BIOS bug safety

For pre-ACPI 3 BIOSes, pre-initialize the end of the e820 buffer just
in case the BIOS returns an unchanged %ecx but without actually
touching the ACPI 3 extended flags field.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---

diff --git a/arch/x86/boot/memory.c b/arch/x86/boot/memory.c
index d5d2360763dc..5054c2ddd1a0 100644
--- a/arch/x86/boot/memory.c
+++ b/arch/x86/boot/memory.c
@@ -31,6 +31,12 @@ static int detect_memory_e820(void)
 	struct e820entry *desc = boot_params.e820_map;
 	static struct e820_ext_entry buf; /* static so it is zeroed */
 
+	/*
+	 * Set this here so that if the BIOS doesn't change this field
+	 * but still doesn't change %ecx, we're still okay...
+	 */
+	buf.ext_flags = 1;
+
 	do {
 		size = sizeof buf;