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>

4 files changed, 19 insertions, 3 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 9a742ce9cc92..8f5f02160ffc 100644
--- a/arch/s390/Kconfig
+++ b/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"
diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 540a67f979b6..68ec4083bf73 100644
--- a/arch/s390/kernel/early.c
+++ b/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
diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 2f35133ebc18..a9d18aafa5f4 100644
--- a/arch/s390/kernel/setup.c
+++ b/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 */
diff --git a/include/asm-s390/setup.h b/include/asm-s390/setup.h
index a76a6b8fd887..aaf4b518b940 100644
--- a/include/asm-s390/setup.h
+++ b/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)