Subject: [PATCH][SVM] Allow direct guest access to PC debug port
From: Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

The PC debug port is used for IO delay and does not require emulation.

Signed-off-by: Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

Index: kernel/drivers/kvm/svm.c
===================================================================
--- kernel.orig/drivers/kvm/svm.c	2007-04-29 10:57:27.219080792 -0500
+++ kernel/drivers/kvm/svm.c	2007-04-29 10:58:37.481399296 -0500
@@ -377,7 +377,7 @@
 	int cpu;
 	struct page *iopm_pages;
 	struct page *msrpm_pages;
-	void *msrpm_va;
+	void *iopm_va, *msrpm_va;
 	int r;
 
 	kvm_emulator_want_group7_invlpg();
@@ -386,8 +386,10 @@
 
 	if (!iopm_pages)
 		return -ENOMEM;
-	memset(page_address(iopm_pages), 0xff,
-					PAGE_SIZE * (1 << IOPM_ALLOC_ORDER));
+
+	iopm_va = page_address(iopm_pages);
+	memset(iopm_va, 0xff, PAGE_SIZE * (1 << IOPM_ALLOC_ORDER));
+	clear_bit(0x80, iopm_va); /* allow direct access to PC debug port */
 	iopm_base = page_to_pfn(iopm_pages) << PAGE_SHIFT;