Linux Virtualization - May 2021 - [RFC][PATCH] vhost/vsock: Add vsock_list file to map cid with vhost tasks

The new trace-cmd 3.0 (which is almost ready to be released) allows for
tracing between host and guests with timestamp synchronization such that
the events on the host and the guest can be interleaved in the proper order
that they occur. KernelShark now has a plugin that visualizes this
interaction.

The implementation requires that the guest has a vsock CID assigned, and on
the guest a "trace-cmd agent" is running, that will listen on a port
for
the CID. The on the host a "trace-cmd record -A guest at cid:port -e
events"
can be called and the host will connect to the guest agent through the
cid/port pair and have the agent enable tracing on behalf of the host and
send the trace data back down to it.

The problem is that there is no sure fire way to find the CID for a guest.
Currently, the user must know the cid, or we have a hack that looks for the
qemu process and parses the --guest-cid parameter from it. But this is
prone to error and does not work on other implementation (was told that
crosvm does not use qemu).

As I can not find a way to discover CIDs assigned to guests via any kernel
interface, I decided to create this one. Note, I'm not attached to it. If
there's a better way to do this, I would love to have it. But since I'm
not
an expert in the networking layer nor virtio, I decided to stick to what I
know and add a debugfs interface that simply lists all the registered CIDs
and the worker task that they are associated with. The worker task at
least has the PID of the task it represents.

Now I can find the cid / host process in charge of the guest pair:

  # cat /sys/kernel/debug/vsock_list
  3	vhost-1954:2002

  # ps aux | grep 1954
  qemu        1954  9.9 21.3 1629092 796148 ?      Sl   16:22   0:58 
/usr/bin/qemu-kvm -name guest=Fedora21,debug-threads=on -S -object
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-1-Fedora21/master-key.aes
-machine pc-1.2,accel=kvm,usb=off,dump-guest-core=off -cpu qemu64 -m 1000
-overcommit mem-lock=off -smp 2,sockets=2,cores=1,threads=1 -uuid
1eefeeb0-3ac7-07c1-926e-236908313b4c -no-user-config -nodefaults -chardev
socket,id=charmonitor,fd=32,server,nowait -mon
chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot
strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device
virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x6 -blockdev
{"driver":"host_device","filename":"/dev/mapper/vg_bxtest-GuestFedora","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}
-blockdev
{"node-name":"libvirt-1-format","read-only":false,"driver":"raw","file":"libvirt-1-storage"}
-device ide-hd,bus=ide.0,unit=0,drive=libvirt-1-
 format,id=ide0-0-0,bootindex=1 -netdev tap,fd=34,id=hostnet0 -device
rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:9f:e9:d5,bus=pci.0,addr=0x3 -netdev
tap,fd=35,id=hostnet1 -device
virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:ec:dc:6e,bus=pci.0,addr=0x5
-chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0
-chardev
pipe,id=charchannel0,path=/var/lib/trace-cmd/virt/Fedora21/trace-pipe-cpu0
-device
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=trace-pipe-cpu0
-chardev
pipe,id=charchannel1,path=/var/lib/trace-cmd/virt/Fedora21/trace-pipe-cpu1
-device
virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=trace-pipe-cpu1
-vnc 127.0.0.1:0 -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 -sandbox
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -device
vhost-vsock-pci,id=vsock0,guest-cid=3,vhostfd=16,bus=pci.0,addr=0x7 -msg
 timestamp=on
  root        2000  0.0  0.0      0     0 ?        S    16:22   0:00
[kvm-pit/1954]
  root        2002  0.0  0.0      0     0 ?        S    16:22   0:00
[vhost-1954]


This is just an example of what I'm looking for. Just a way to find what
process is using what cid.

Signed-off-by: Steven Rostedt (VMware) <rostedt at goodmis.org>
---
diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 5e78fb719602..4f03b25b23c1 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -15,6 +15,7 @@
 #include <linux/virtio_vsock.h>
 #include <linux/vhost.h>
 #include <linux/hashtable.h>
+#include <linux/debugfs.h>
 
 #include <net/af_vsock.h>
 #include "vhost.h"
@@ -900,6 +901,128 @@ static struct miscdevice vhost_vsock_misc = {
 	.fops = &vhost_vsock_fops,
 };
 
+static struct dentry *vsock_file;
+
+struct vsock_file_iter {
+	struct hlist_node	*node;
+	int			index;
+};
+
+
+static void *vsock_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct vsock_file_iter *iter = v;
+	struct vhost_vsock *vsock;
+
+	if (pos)
+		(*pos)++;
+
+	if (iter->index >= (int)HASH_SIZE(vhost_vsock_hash))
+		return NULL;
+
+	if (iter->node)
+		iter->node = rcu_dereference_raw(hlist_next_rcu(iter->node));
+
+	for (;;) {
+		if (iter->node) {
+			vsock = hlist_entry_safe(rcu_dereference_raw(iter->node),
+						 struct vhost_vsock, hash);
+			if (vsock->guest_cid)
+				break;
+			iter->node = rcu_dereference_raw(hlist_next_rcu(iter->node));
+			continue;
+		}
+		iter->index++;
+		if (iter->index >= HASH_SIZE(vhost_vsock_hash))
+			return NULL;
+
+		iter->node =
rcu_dereference_raw(hlist_first_rcu(&vhost_vsock_hash[iter->index]));
+	}
+	return iter;
+}
+
+static void *vsock_start(struct seq_file *m, loff_t *pos)
+{
+	struct vsock_file_iter *iter = m->private;
+	loff_t l = 0;
+	void *t;
+
+	rcu_read_lock();
+
+	iter->index = -1;
+	iter->node = NULL;
+	t = vsock_next(m, iter, NULL);
+
+	for (; iter->index < HASH_SIZE(vhost_vsock_hash) && l < *pos;
+	     t = vsock_next(m, iter, &l))
+		;
+
+	return t;
+}
+
+static void vsock_stop(struct seq_file *m, void *p)
+{
+	rcu_read_unlock();
+}
+
+static int vsock_show(struct seq_file *m, void *v)
+{
+	struct vsock_file_iter *iter = v;
+	struct vhost_vsock *vsock;
+	struct task_struct *worker;
+
+	if (!iter || iter->index >= HASH_SIZE(vhost_vsock_hash))
+		return 0;
+
+	vsock = hlist_entry_safe(rcu_dereference_raw(iter->node), struct
vhost_vsock, hash);
+	worker = vsock->dev.worker;
+	seq_printf(m, "%d\t", vsock->guest_cid);
+
+	if (worker)
+		seq_printf(m, "%s:%d\n", worker->comm, worker->pid);
+	else
+		seq_puts(m, "(no task)\n");
+
+	return 0;
+}
+
+static const struct seq_operations vsock_file_seq_ops = {
+	.start		= vsock_start,
+	.next		= vsock_next,
+	.stop		= vsock_stop,
+	.show		= vsock_show,
+};
+
+static int vsock_file_open(struct inode *inode, struct file *file)
+{
+	struct vsock_file_iter *iter;
+	struct seq_file *m;
+	int ret;
+
+	iter = kzalloc(sizeof(*iter), GFP_KERNEL);
+	if (!iter)
+		return -ENOMEM;
+
+	ret = seq_open(file, &vsock_file_seq_ops);
+	if (ret) {
+		kfree(iter);
+		return ret;
+	}
+
+	m = file->private_data;
+	m->private = iter;
+
+	return 0;
+}
+
+static const struct file_operations vsock_file_fops = {
+	.owner		= THIS_MODULE,
+	.open		= vsock_file_open,
+	.release	= seq_release_private,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+};
+
 static int __init vhost_vsock_init(void)
 {
 	int ret;
@@ -908,12 +1031,15 @@ static int __init vhost_vsock_init(void)
 				  VSOCK_TRANSPORT_F_H2G);
 	if (ret < 0)
 		return ret;
+	vsock_file = debugfs_create_file("vsock_list", 0400,
+					 NULL, NULL, &vsock_file_fops);
 	return misc_register(&vhost_vsock_misc);
 };
 
 static void __exit vhost_vsock_exit(void)
 {
 	misc_deregister(&vhost_vsock_misc);
+	debugfs_remove(vsock_file);
 	vsock_core_unregister(&vhost_transport.transport);
 };

For kicks, I wrote this program that uses libtracefs to search all CIDS
(1-255), and find the kvm guests that are attached to them.

It traces the sched_wakeup and kvm_exit, looking for:

 this_task -> wakeup -> wakeup -> kvm_exit

when doing a connect to a cid.

When it finds the pid that did a kvm_exit, it knows that's the PID that
is woken by the vhost worker task. It's a little slow, and I would
really like a better way to do this, but it's at least an option that
is available now.

-- Steve
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Hi Steven,

On Wed, May 05, 2021 at 04:38:55PM -0400, Steven Rostedt
wrote:
>The new trace-cmd 3.0 (which is almost ready to be released) allows for
>tracing between host and guests with timestamp synchronization such that
>the events on the host and the guest can be interleaved in the proper order
>that they occur. KernelShark now has a plugin that visualizes this
>interaction.
>
>The implementation requires that the guest has a vsock CID assigned, and on
>the guest a "trace-cmd agent" is running, that will listen on a
port for
>the CID. The on the host a "trace-cmd record -A guest at cid:port -e
events"
>can be called and the host will connect to the guest agent through the
>cid/port pair and have the agent enable tracing on behalf of the host and
>send the trace data back down to it.
>
>The problem is that there is no sure fire way to find the CID for a guest.
>Currently, the user must know the cid, or we have a hack that looks for the
>qemu process and parses the --guest-cid parameter from it. But this is
>prone to error and does not work on other implementation (was told that
>crosvm does not use qemu).
For debug I think could be useful to link the vhost-vsock kthread to the 
CID, but for the user point of view, maybe is better to query the VM 
management layer, for example if you're using libvirt, you can easily do:

$ virsh dumpxml fedora34 | grep cid
     <cid auto='yes' address='3'/>
>
>As I can not find a way to discover CIDs assigned to guests via any kernel
>interface, I decided to create this one. Note, I'm not attached to it.
If
>there's a better way to do this, I would love to have it. But since
I'm not
>an expert in the networking layer nor virtio, I decided to stick to what I
>know and add a debugfs interface that simply lists all the registered 
>CIDs
>and the worker task that they are associated with. The worker task at
>least has the PID of the task it represents.
I honestly don't know if it's the best interface, like I said maybe for 
debugging it's fine, but if we want to expose it to the user in some 
way, we could support devlink/netlink to provide information about the 
vsock devices currently in use.
>
>Now I can find the cid / host process in charge of the guest pair:
>
>  # cat /sys/kernel/debug/vsock_list
>  3	vhost-1954:2002
>
>  # ps aux | grep 1954
>  qemu        1954  9.9 21.3 1629092 796148 ?      Sl   16:22   0:58 
/usr/bin/qemu-kvm -name guest=Fedora21,debug-threads=on -S -object
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-1-Fedora21/master-key.aes
-machine pc-1.2,accel=kvm,usb=off,dump-guest-core=off -cpu qemu64 -m 1000
-overcommit mem-lock=off -smp 2,sockets=2,cores=1,threads=1 -uuid
1eefeeb0-3ac7-07c1-926e-236908313b4c -no-user-config -nodefaults -chardev
socket,id=charmonitor,fd=32,server,nowait -mon
chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot
strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device
virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x6 -blockdev
{"driver":"host_device","filename":"/dev/mapper/vg_bxtest-GuestFedora","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}
-blockdev
{"node-name":"libvirt-1-format","read-only":false,"driver":"raw","file":"libvirt-1-storage"}
-device ide-hd,bus=ide.0,unit=0,drive=libvirt-1-
> format,id=ide0-0-0,bootindex=1 -netdev tap,fd=34,id=hostnet0 -device
rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:9f:e9:d5,bus=pci.0,addr=0x3 -netdev
tap,fd=35,id=hostnet1 -device
virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:ec:dc:6e,bus=pci.0,addr=0x5
-chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0
-chardev
pipe,id=charchannel0,path=/var/lib/trace-cmd/virt/Fedora21/trace-pipe-cpu0
-device
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=trace-pipe-cpu0
-chardev
pipe,id=charchannel1,path=/var/lib/trace-cmd/virt/Fedora21/trace-pipe-cpu1
-device
virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=trace-pipe-cpu1
-vnc 127.0.0.1:0 -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 -sandbox
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -device
vhost-vsock-pci,id=vsock0,guest-cid=3,vhostfd=16,bus=pci.0,addr=0x7 -msg
> timestamp=on
>  root        2000  0.0  0.0      0     0 ?        S    16:22   0:00
[kvm-pit/1954]
>  root        2002  0.0  0.0      0     0 ?        S    16:22   0:00
[vhost-1954]
>
>
>This is just an example of what I'm looking for. Just a way to find what
>process is using what cid.
>
>Signed-off-by: Steven Rostedt (VMware) <rostedt at goodmis.org>
>---
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index 5e78fb719602..4f03b25b23c1 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -15,6 +15,7 @@
> #include <linux/virtio_vsock.h>
> #include <linux/vhost.h>
> #include <linux/hashtable.h>
>+#include <linux/debugfs.h>
>
> #include <net/af_vsock.h>
> #include "vhost.h"
>@@ -900,6 +901,128 @@ static struct miscdevice vhost_vsock_misc = {
> 	.fops = &vhost_vsock_fops,
> };
>
>+static struct dentry *vsock_file;
>+
>+struct vsock_file_iter {
>+	struct hlist_node	*node;
>+	int			index;
>+};
>+
>+
>+static void *vsock_next(struct seq_file *m, void *v, loff_t *pos)
>+{
>+	struct vsock_file_iter *iter = v;
>+	struct vhost_vsock *vsock;
>+
>+	if (pos)
>+		(*pos)++;
>+
>+	if (iter->index >= (int)HASH_SIZE(vhost_vsock_hash))
>+		return NULL;
>+
>+	if (iter->node)
>+		iter->node = rcu_dereference_raw(hlist_next_rcu(iter->node));
>+
>+	for (;;) {
>+		if (iter->node) {
>+			vsock = hlist_entry_safe(rcu_dereference_raw(iter->node),
>+						 struct vhost_vsock, hash);
>+			if (vsock->guest_cid)
>+				break;
>+			iter->node = rcu_dereference_raw(hlist_next_rcu(iter->node));
>+			continue;
>+		}
>+		iter->index++;
>+		if (iter->index >= HASH_SIZE(vhost_vsock_hash))
>+			return NULL;
>+
>+		iter->node =
rcu_dereference_raw(hlist_first_rcu(&vhost_vsock_hash[iter->index]));
>+	}
>+	return iter;
>+}
>+
>+static void *vsock_start(struct seq_file *m, loff_t *pos)
>+{
>+	struct vsock_file_iter *iter = m->private;
>+	loff_t l = 0;
>+	void *t;
>+
>+	rcu_read_lock();
Instead of keeping this rcu lock between vsock_start() and vsock_stop(), 
maybe it's better to make a dump here of the bindings (pid/cid), save it 
in an array, and iterate it in vsock_next().
>+
>+	iter->index = -1;
>+	iter->node = NULL;
>+	t = vsock_next(m, iter, NULL);
>+
>+	for (; iter->index < HASH_SIZE(vhost_vsock_hash) && l <
*pos;
>+	     t = vsock_next(m, iter, &l))
>+		;
A while() maybe was more readable...

Thanks,
Stefano

On 5/5/21 3:38 PM, Steven Rostedt wrote:
> The new trace-cmd 3.0 (which is almost ready to be released) allows for
> tracing between host and guests with timestamp synchronization such that
> the events on the host and the guest can be interleaved in the proper order
> that they occur. KernelShark now has a plugin that visualizes this
> interaction.
> 
> The implementation requires that the guest has a vsock CID assigned, and on
> the guest a "trace-cmd agent" is running, that will listen on a
port for
> the CID. The on the host a "trace-cmd record -A guest at cid:port -e
events"
> can be called and the host will connect to the guest agent through the
> cid/port pair and have the agent enable tracing on behalf of the host and
> send the trace data back down to it.
> 
> The problem is that there is no sure fire way to find the CID for a guest.
> Currently, the user must know the cid, or we have a hack that looks for the
> qemu process and parses the --guest-cid parameter from it. But this is
> prone to error and does not work on other implementation (was told that
> crosvm does not use qemu).
> 
> As I can not find a way to discover CIDs assigned to guests via any kernel
> interface, I decided to create this one. Note, I'm not attached to it.
If
> there's a better way to do this, I would love to have it. But since
I'm not
> an expert in the networking layer nor virtio, I decided to stick to what I
> know and add a debugfs interface that simply lists all the registered CIDs
> and the worker task that they are associated with. The worker task at
> least has the PID of the task it represents.
> 
> Now I can find the cid / host process in charge of the guest pair:
> 
>   # cat /sys/kernel/debug/vsock_list
>   3	vhost-1954:2002
> 
I think I need the same thing for vhost-scsi. We want to know a vhost-scsi
devs worker thread's pid. If we use multiple vhost-devs in one VM then we
wanted to be able to know which thread goes with which dev.

For the vhost thread patches I added an ioctl:

https://lists.linuxfoundation.org/pipermail/virtualization/2021-April/054014.html

but I had originally implemented it in sysfs. For sysfs we can add a struct
device in the vhost_dev and struct deice in the vhost_virtqueue. We then
have a 2 new classes /sys/class/vhost_device and vhost_virtqueue with the
vhost_device device the parent of vhost_virtqueue device.

The nice thing is that it's a common interface and works for every vhost_dev
and all their virtqueues. It works for non libvirt users.

The drawback is adding in refcounts/releases and that type of code for the
vhost_dev and vhost_virtqueue. Also I'm not sure about security.

Note that I'm not tied to sysfs. netlink would be fine. I just need any
interface.

On Wed, May 05, 2021 at 04:38:55PM -0400, Steven Rostedt
wrote:
> The new trace-cmd 3.0 (which is almost ready to be released) allows for
> tracing between host and guests with timestamp synchronization such that
> the events on the host and the guest can be interleaved in the proper order
> that they occur. KernelShark now has a plugin that visualizes this
> interaction.
> 
> The implementation requires that the guest has a vsock CID assigned, and on
> the guest a "trace-cmd agent" is running, that will listen on a
port for
> the CID. The on the host a "trace-cmd record -A guest at cid:port -e
events"
> can be called and the host will connect to the guest agent through the
> cid/port pair and have the agent enable tracing on behalf of the host and
> send the trace data back down to it.
> 
> The problem is that there is no sure fire way to find the CID for a guest.
> Currently, the user must know the cid, or we have a hack that looks for the
> qemu process and parses the --guest-cid parameter from it. But this is
> prone to error and does not work on other implementation (was told that
> crosvm does not use qemu).
The crosvm command-line syntax is: crosvm run --cid <CID>
> As I can not find a way to discover CIDs assigned to guests via any kernel
> interface, I decided to create this one. Note, I'm not attached to it.
If
> there's a better way to do this, I would love to have it. But since
I'm not
> an expert in the networking layer nor virtio, I decided to stick to what I
> know and add a debugfs interface that simply lists all the registered CIDs
> and the worker task that they are associated with. The worker task at
> least has the PID of the task it represents.
> 
> Now I can find the cid / host process in charge of the guest pair:
> 
>   # cat /sys/kernel/debug/vsock_list
>   3	vhost-1954:2002
> 
>   # ps aux | grep 1954
>   qemu        1954  9.9 21.3 1629092 796148 ?      Sl   16:22   0:58 
/usr/bin/qemu-kvm -name guest=Fedora21,debug-threads=on -S -object
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-1-Fedora21/master-key.aes
-machine pc-1.2,accel=kvm,usb=off,dump-guest-core=off -cpu qemu64 -m 1000
-overcommit mem-lock=off -smp 2,sockets=2,cores=1,threads=1 -uuid
1eefeeb0-3ac7-07c1-926e-236908313b4c -no-user-config -nodefaults -chardev
socket,id=charmonitor,fd=32,server,nowait -mon
chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot
strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device
virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x6 -blockdev
{"driver":"host_device","filename":"/dev/mapper/vg_bxtest-GuestFedora","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}
-blockdev
{"node-name":"libvirt-1-format","read-only":false,"driver":"raw","file":"libvirt-1-storage"}
-device ide-hd,bus=ide.0,unit=0,drive=libvirt-1-
>  format,id=ide0-0-0,bootindex=1 -netdev tap,fd=34,id=hostnet0 -device
rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:9f:e9:d5,bus=pci.0,addr=0x3 -netdev
tap,fd=35,id=hostnet1 -device
virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:ec:dc:6e,bus=pci.0,addr=0x5
-chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0
-chardev
pipe,id=charchannel0,path=/var/lib/trace-cmd/virt/Fedora21/trace-pipe-cpu0
-device
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=trace-pipe-cpu0
-chardev
pipe,id=charchannel1,path=/var/lib/trace-cmd/virt/Fedora21/trace-pipe-cpu1
-device
virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=trace-pipe-cpu1
-vnc 127.0.0.1:0 -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 -sandbox
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -device
vhost-vsock-pci,id=vsock0,guest-cid=3,vhostfd=16,bus=pci.0,addr=0x7 -msg
>  timestamp=on
>   root        2000  0.0  0.0      0     0 ?        S    16:22   0:00
[kvm-pit/1954]
>   root        2002  0.0  0.0      0     0 ?        S    16:22   0:00
[vhost-1954]
This approach relies on process hierarchy of the VMM (QEMU).
Multi-process QEMU is in development and will allow VIRTIO devices to
run as separate processes from the main QEMU. It then becomes harder to
correlate a VIRTIO device process with its QEMU process.

So I think in the end this approach ends up being as fragile as parsing
command-lines. The kernel doesn't really have the concept of a
"VM" that
the vhost_vsock is associated with :). Maybe just parse QEMU and crosvm
command-lines?

Stefan
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