From 3e89a76fee8edfbeb3d069f7d2f04df7fa34ecc3 Mon Sep 17 00:00:00 2001
From: Vladimir Serbinenko <phcoder@gmail.com>
Date: Sun, 10 Jan 2016 13:48:26 +0100
Subject: [PATCH] Add wbinvd around bios call.

Via C3 has problems with cache coherency when transitioning between the modes,
so flush it around bios calls.
---
 grub-core/kern/i386/int.S     | 11 +++++++++++
 grub-core/kern/i386/pc/init.c | 24 ++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/grub-core/kern/i386/int.S b/grub-core/kern/i386/int.S
index 7edace404..862a54202 100644
--- a/grub-core/kern/i386/int.S
+++ b/grub-core/kern/i386/int.S
@@ -44,6 +44,13 @@ FUNCTION(grub_bios_interrupt)
 	movl 	24(%edx), %esi
 	movl 	28(%edx), %edx
 
+	/*
+	Via C3 CPUs have cache coherence problems, so we need to call
+	wbinvd at these 2 points. As wbinvd slows down boot, don't do
+	it on non-VIA. 9090 is nop nop. */
+VARIABLE(grub_bios_via_workaround1)
+	.byte 0x90, 0x90
+
 	PROT_TO_REAL
 	.code16
 	pushf
@@ -92,6 +99,10 @@ intno:
 	movw	%ax, LOCAL(bios_register_es)
 
 	popf
+
+VARIABLE(grub_bios_via_workaround2)
+	.byte 0x90, 0x90
+
 	REAL_TO_PROT
 	.code32
 
diff --git a/grub-core/kern/i386/pc/init.c b/grub-core/kern/i386/pc/init.c
index 3c8160aab..27bc68b8a 100644
--- a/grub-core/kern/i386/pc/init.c
+++ b/grub-core/kern/i386/pc/init.c
@@ -32,6 +32,7 @@
 #include <grub/env.h>
 #include <grub/cache.h>
 #include <grub/time.h>
+#include <grub/cpu/cpuid.h>
 #include <grub/cpu/tsc.h>
 #include <grub/machine/time.h>
 
@@ -184,6 +185,26 @@ mmap_iterate_hook (grub_uint64_t addr, grub_uint64_t size,
   return 0;
 }
 
+extern grub_uint16_t grub_bios_via_workaround1, grub_bios_via_workaround2;
+
+/* Via needs additional wbinvd.  */
+static void
+grub_via_workaround_init (void)
+{
+  grub_uint32_t manufacturer[3], max_cpuid;
+  if (! grub_cpu_is_cpuid_supported ())
+    return;
+
+  grub_cpuid (0, max_cpuid, manufacturer[0], manufacturer[2], manufacturer[1]);
+
+  if (grub_memcmp (manufacturer, "CentaurHauls", 12) != 0)
+    return;
+
+  grub_bios_via_workaround1 = 0x090f;
+  grub_bios_via_workaround2 = 0x090f;
+  asm volatile ("wbinvd");
+}
+
 void
 grub_machine_init (void)
 {
@@ -193,6 +214,9 @@ grub_machine_init (void)
 #endif
   grub_addr_t modend;
 
+  /* This has to happen before any BIOS calls. */
+  grub_via_workaround_init ();
+
   grub_modbase = GRUB_MEMORY_MACHINE_DECOMPRESSION_ADDR + (_edata - _start);
 
   /* Initialize the console as early as possible.  */
-- 
2.47.2