Linux Virtualization - Aug 2010 - [PATCH 1/3] S390: take a full byte as ext_param indicator

Currenty the ext_param field only distinguishes between "config
change" and
"vring interrupt". We can do a lot more with it though, so let's
enable a
full byte of possible values and constants to #defines while at it.

Signed-off-by: Alexander Graf <agraf at suse.de>

---

v1 -> v2:

  - move defines to virtio_s390.h
---
 arch/s390/include/asm/kvm_virtio.h |    6 ++++++
 drivers/s390/kvm/kvm_virtio.c      |   19 +++++++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/arch/s390/include/asm/kvm_virtio.h
b/arch/s390/include/asm/kvm_virtio.h
index acdfdff..3f5d100 100644
--- a/arch/s390/include/asm/kvm_virtio.h
+++ b/arch/s390/include/asm/kvm_virtio.h
@@ -54,4 +54,10 @@ struct kvm_vqconfig {
  * This is pagesize for historical reasons. */
 #define KVM_S390_VIRTIO_RING_ALIGN	4096
 
+
+/* These values are supposed to be in ext_params on an interrupt */
+#define VIRTIO_PARAM_MASK		0xff
+#define VIRTIO_PARAM_VRING_INTERRUPT	0x0
+#define VIRTIO_PARAM_CONFIG_CHANGED	0x1
+
 #endif
diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index 4e298bc..68cef4d 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -334,7 +334,7 @@ static void kvm_extint_handler(u16 code)
 {
 	struct virtqueue *vq;
 	u16 subcode;
-	int config_changed;
+	u32 param;
 
 	subcode = S390_lowcore.cpu_addr;
 	if ((subcode & 0xff00) != VIRTIO_SUBCODE_64)
@@ -343,18 +343,25 @@ static void kvm_extint_handler(u16 code)
 	/* The LSB might be overloaded, we have to mask it */
 	vq = (struct virtqueue *)(S390_lowcore.ext_params2 & ~1UL);
 
-	/* We use the LSB of extparam, to decide, if this interrupt is a config
-	 * change or a "standard" interrupt */
-	config_changed = S390_lowcore.ext_params & 1;
+	/* We use ext_params to decide what this interrupt means */
+	param = S390_lowcore.ext_params & VIRTIO_PARAM_MASK;
 
-	if (config_changed) {
+	switch (param) {
+	case VIRTIO_PARAM_CONFIG_CHANGED:
+	{
 		struct virtio_driver *drv;
 		drv = container_of(vq->vdev->dev.driver,
 				   struct virtio_driver, driver);
 		if (drv->config_changed)
 			drv->config_changed(vq->vdev);
-	} else
+
+		break;
+	}
+	case VIRTIO_PARAM_VRING_INTERRUPT:
+	default:
 		vring_interrupt(0, vq);
+		break;
+	}
 }
 
 /*
-- 
1.6.0.2

The one big missing feature in s390-virtio was hotplugging. This is no more.
This patch implements hotplug add support, so you can on the fly add new devices
in the guest.

Keep in mind that this needs a patch for qemu to actually leverage the
functionality.

Signed-off-by: Alexander Graf <agraf at suse.de>

---

v1 -> v2:

  - move dev_add to kvm_virtio.h
---
 arch/s390/include/asm/kvm_virtio.h |    1 +
 drivers/s390/kvm/kvm_virtio.c      |   47 ++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 0 deletions(-)

diff --git a/arch/s390/include/asm/kvm_virtio.h
b/arch/s390/include/asm/kvm_virtio.h
index 3f5d100..72f6141 100644
--- a/arch/s390/include/asm/kvm_virtio.h
+++ b/arch/s390/include/asm/kvm_virtio.h
@@ -59,5 +59,6 @@ struct kvm_vqconfig {
 #define VIRTIO_PARAM_MASK		0xff
 #define VIRTIO_PARAM_VRING_INTERRUPT	0x0
 #define VIRTIO_PARAM_CONFIG_CHANGED	0x1
+#define VIRTIO_PARAM_DEV_ADD		0x2
 
 #endif
diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index 68cef4d..5a46b8c 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -32,6 +32,7 @@
  * The pointer to our (page) of device descriptions.
  */
 static void *kvm_devices;
+struct work_struct hotplug_work;
 
 struct kvm_device {
 	struct virtio_device vdev;
@@ -328,6 +329,47 @@ static void scan_devices(void)
 }
 
 /*
+ * match for a kvm device with a specific desc pointer
+ */
+static int match_desc(struct device *dev, void *data)
+{
+	if ((ulong)to_kvmdev(dev_to_virtio(dev))->desc == (ulong)data)
+		return 1;
+
+	return 0;
+}
+
+/*
+ * hotplug_device tries to find changes in the device page.
+ */
+static void hotplug_devices(struct work_struct *dummy)
+{
+	unsigned int i;
+	struct kvm_device_desc *d;
+	struct device *dev;
+
+	for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
+		d = kvm_devices + i;
+
+		/* end of list */
+		if (d->type == 0)
+			break;
+
+		/* device already exists */
+		dev = device_find_child(kvm_root, d, match_desc);
+		if (dev) {
+			/* XXX check for hotplug remove */
+			put_device(dev);
+			continue;
+		}
+
+		/* new device */
+		printk(KERN_INFO "Adding new virtio device %p\n", d);
+		add_kvm_device(d, i);
+	}
+}
+
+/*
  * we emulate the request_irq behaviour on top of s390 extints
  */
 static void kvm_extint_handler(u16 code)
@@ -357,6 +399,9 @@ static void kvm_extint_handler(u16 code)
 
 		break;
 	}
+	case VIRTIO_PARAM_DEV_ADD:
+		schedule_work(&hotplug_work);
+		break;
 	case VIRTIO_PARAM_VRING_INTERRUPT:
 	default:
 		vring_interrupt(0, vq);
@@ -390,6 +435,8 @@ static int __init kvm_devices_init(void)
 
 	kvm_devices = (void *) real_memory_size;
 
+	INIT_WORK(&hotplug_work, hotplug_devices);
+
 	ctl_set_bit(0, 9);
 	register_external_interrupt(0x2603, kvm_extint_handler);
 
-- 
1.6.0.2

As suggested by Christian, we should expose headers to user space with
information that might be valuable there. The s390 virtio interface is
one of those cases. It defines an ABI between hypervisor and guest, so
it should be exposed to user space.

Reported-by: Christian Borntraeger <borntraeger at de.ibm.com>
Signed-off-by: Alexander Graf <agraf at suse.de>
---
 arch/s390/include/asm/Kbuild |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/arch/s390/include/asm/Kbuild b/arch/s390/include/asm/Kbuild
index 63a2341..ee7937d 100644
--- a/arch/s390/include/asm/Kbuild
+++ b/arch/s390/include/asm/Kbuild
@@ -8,6 +8,7 @@ header-y += ucontext.h
 header-y += vtoc.h
 header-y += zcrypt.h
 header-y += chsc.h
+header-y += kvm_virtio.h
 
 unifdef-y += cmb.h
 unifdef-y += debug.h
-- 
1.6.0.2

On Tue, Aug 24, 2010 at 03:48:50PM +0200, Alexander Graf
wrote:
> Currenty the ext_param field only distinguishes between "config
change" and
> "vring interrupt". We can do a lot more with it though, so
let's enable a
> full byte of possible values and constants to #defines while at it.
> 
> Signed-off-by: Alexander Graf <agraf at suse.de>
> 
> ---
> 
> v1 -> v2:
> 
>   - move defines to virtio_s390.h
> ---
>  arch/s390/include/asm/kvm_virtio.h |    6 ++++++
>  drivers/s390/kvm/kvm_virtio.c      |   19 +++++++++++++------
>  2 files changed, 19 insertions(+), 6 deletions(-)
Applied, thanks.

On 24.08.2010, at 15:48, Alexander Graf wrote:
> The one big missing feature in s390-virtio was hotplugging. This is no
more.
> This patch implements hotplug add support, so you can on the fly add new
devices
> in the guest.
> 
> Keep in mind that this needs a patch for qemu to actually leverage the
> functionality.
> 
> Signed-off-by: Alexander Graf <agraf at suse.de>
ping (on the patch set)?


Alex