kvm: Setup fake IVT table

Setup fake interrupt handlers for real mode, it consists of iret opcode only.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

ivt.c

@@ -36,3 +36,11 @@ void ivt_set_entry(struct ivt_entry e, unsigned int n)
 	if (n < IVT_VECTORS)
 		ivt_table[n] = e;
 }
+
+void ivt_set_all(struct ivt_entry e)
+{
+	unsigned int i;
+
+	for (i = 0; i < IVT_VECTORS; i++)
+		ivt_table[i] = e;
+}

ivt.h

@@ -5,11 +5,12 @@
 #define IVT_VECTORS	256
 
 struct ivt_entry {
-	uint16_t segment;
 	uint16_t offset;
+	uint16_t segment;
 } __attribute__((packed));
 
 void ivt_reset(void);
 void ivt_copy_table(void *dst, unsigned int size);
 struct ivt_entry * const ivt_get_entry(unsigned int n);
 void ivt_set_entry(struct ivt_entry e, unsigned int n);
+void ivt_set_all(struct ivt_entry e);

kvm.c

@@ -16,6 +16,7 @@
 #include <stdio.h>
 #include <fcntl.h>
 
+#include "ivt.h"
 #include "util.h"
 
 /*
@@ -198,6 +199,7 @@ static bool load_bzimage(struct kvm *self, int fd, const char *kernel_cmdline)
 {
 	unsigned long setup_sects;
 	struct boot_params boot;
+	struct ivt_entry real_mode_irq;
 	ssize_t setup_size;
 	void *p;
 	int nr;
@@ -241,6 +243,20 @@ static bool load_bzimage(struct kvm *self, int fd, const char *kernel_cmdline)
 	self->boot_ip		= BOOT_LOADER_IP + 0x200;
 	self->boot_sp		= BOOT_LOADER_SP;
 
+	/*
+	 * Setup a *fake* real mode IVT, it has only one real
+	 * hadler which does just iret
+	 */
+	real_mode_irq = (struct ivt_entry) {
+		.segment	= 0,
+		.offset		= 0x400 + 1,
+	};
+	ivt_set_all(real_mode_irq);
+	p = guest_flat_to_host(self, 0);
+	ivt_copy_table(p, IVT_VECTORS * sizeof(real_mode_irq));
+	p += IVT_VECTORS * sizeof(real_mode_irq) + 1;
+	*(char *)p = 0xcf; /* iret here */
+
 	return true;
 }