[PATCH docs v3 2/3] qm: add document section for the pvpanic device

[Kaiyang Wu <wukaiyang2003@gmail.com>]

Document the pvpanic device and corresponding driver requirements on
different VMs.

Signed-off-by: Kaiyang Wu <wukaiyang@loongfans.cn>
---
 qm.adoc | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/qm.adoc b/qm.adoc
index 18a4fbe..5972fea 100644
--- a/qm.adoc
+++ b/qm.adoc
@@ -1476,6 +1476,44 @@ tag (name used to mount the device on the guest).
 For more information on available virtiofsd parameters, see the
 https://gitlab.com/virtio-fs/virtiofsd[GitLab virtiofsd project page].
 
+[[qm_pvpanic]]
+Pvpanic
+~~~~~~~
+
+Pvpanic is a device to send system panic events to QEMU. It allows to
+provide extra VM status and execute the specified panic action when the VM
+system crashes.
+
+To add a pvpanic device run the following command:
+
+----
+qm set <vmid> -pvpanic enabled=1[,action=<action>]
+----
+
+A panic action can be specified to perform when the VM system crashes. Available
+panic actions are:
+
+* `none`: Continue VM execution
+* `pause`: Pause the VM
+* `shutdown`: Shutdown the VM and exit, according to the shutdown action
+* `exit-failure`: Shutdown the VM and exit with non-zero status
+
+NOTE: The default panic action is `shutdown`. However, because the shutdown
+action is set to `pause` by default, `shutdown` and `pause` both pause the
+VM unless manually specifying the shutdown action using custom `args`.
+
+NOTE: VMs managed by the HA stack can set `exit-failure` to exit the QEMU
+process completely and let the HA stack start it again.
+
+Linux VMs with kernel >=5.2 support pvpanic PCI device by default
+(https://www.kernelconfig.io/CONFIG_PVPANIC_PCI[pvpanic PCI driver]).
+
+Windows VMs require
+https://github.com/virtio-win/kvm-guest-drivers-windows/[kvm-guest-drivers-windows]
+to use pvpanic.
+
+FreeBSD VMs do not support pvpanic.
+
 [[qm_bootorder]]
 Device Boot Order
 ~~~~~~~~~~~~~~~~~
-- 
2.56.0