s390: KVM guest: detect when running on kvm

This patch adds functionality to detect if the kernel runs under the KVM
hypervisor. A macro MACHINE_IS_KVM is exported for device drivers. This
allows drivers to skip device detection if the systems runs non-virtualized.
We also define a preferred console to avoid having the ttyS0, which is a line
mode only console.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/s390/Kconfig

@@ -520,6 +520,13 @@ config ZFCPDUMP
 	  Select this option if you want to build an zfcpdump enabled kernel.
 	  Refer to <file:Documentation/s390/zfcpdump.txt> for more details on this.
 
+config S390_GUEST
+bool "s390 guest support (EXPERIMENTAL)"
+	depends on 64BIT && EXPERIMENTAL
+	select VIRTIO
+	select VIRTIO_RING
+	help
+	  Select this option if you want to run the kernel under s390 linux
 endmenu
 
 source "net/Kconfig"

arch/s390/kernel/early.c

@@ -144,6 +144,10 @@ static noinline __init void detect_machine_type(void)
 	/* Running on a P/390 ? */
 	if (cpuinfo->cpu_id.machine == 0x7490)
 		machine_flags |= 4;
+
+	/* Running under KVM ? */
+	if (cpuinfo->cpu_id.version == 0xfe)
+		machine_flags |= 64;
 }
 
 #ifdef CONFIG_64BIT

arch/s390/kernel/setup.c

@@ -801,9 +801,13 @@ setup_arch(char **cmdline_p)
 	       "This machine has an IEEE fpu\n" :
 	       "This machine has no IEEE fpu\n");
 #else /* CONFIG_64BIT */
-	printk((MACHINE_IS_VM) ?
-	       "We are running under VM (64 bit mode)\n" :
-	       "We are running native (64 bit mode)\n");
+	if (MACHINE_IS_VM)
+		printk("We are running under VM (64 bit mode)\n");
+	else if (MACHINE_IS_KVM) {
+		printk("We are running under KVM (64 bit mode)\n");
+		add_preferred_console("ttyS", 1, NULL);
+	} else
+		printk("We are running native (64 bit mode)\n");
 #endif /* CONFIG_64BIT */
 
 	/* Save unparsed command line copy for /proc/cmdline */

include/asm-s390/setup.h

@@ -62,6 +62,7 @@ extern unsigned long machine_flags;
 #define MACHINE_IS_VM		(machine_flags & 1)
 #define MACHINE_IS_P390		(machine_flags & 4)
 #define MACHINE_HAS_MVPG	(machine_flags & 16)
+#define MACHINE_IS_KVM		(machine_flags & 64)
 #define MACHINE_HAS_IDTE	(machine_flags & 128)
 #define MACHINE_HAS_DIAG9C	(machine_flags & 256)