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s390x/vfio-ap: document hot plug/unplug of vfio-ap device

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Let's update the vfio-ap.txt document to include the hot plug/unplug
support.

Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Message-Id: <1550519397-25359-3-git-send-email-akrowiak@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
This commit is contained in:
Tony Krowiak 2019-02-18 14:49:57 -05:00 committed by Cornelia Huck
parent 374b78e370
commit bac03ec72f
1 changed files with 56 additions and 5 deletions
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docs/vfio-ap.txt
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@ -440,8 +440,7 @@ unassign_control_domain
'unassign_domain' file. This may be done multiple times to unassign more than
one control domain.
Notes: Hot plug/unplug is not currently supported for mediated AP matrix
devices, so no changes to the AP matrix will be allowed while a guest using
Notes: No changes to the AP matrix will be allowed while a guest using
the mediated matrix device is running. Attempts to assign an adapter,
domain or control domain will be rejected and an error (EBUSY) returned.
@ -562,6 +561,54 @@ facilities:
for guest usage, no AP devices can be made accessible to a
guest started without APFT installed.
Hot plug a vfio-ap device into a running guest:
==============================================
Only one vfio-ap device can be attached to the virtual machine's ap-bus, so a
vfio-ap device can be hot plugged if and only if no vfio-ap device is attached
to the bus already, whether via the QEMU command line or a prior hot plug
action.
To hot plug a vfio-ap device, use the QEMU device_add command:
(qemu) device_add vfio-ap,sysfsdev="$path-to-mdev"
Where the '$path-to-mdev' value specifies the absolute path to a mediated
device to which AP resources to be used by the guest have been assigned.
Note that on Linux guests, the AP devices will be created in the
/sys/bus/ap/devices directory when the AP bus subsequently performs its periodic
scan, so there may be a short delay before the AP devices are accessible on the
guest.
The command will fail if:
* A vfio-ap device has already been attached to the virtual machine's ap-bus.
* The CPU model features for controlling guest access to AP facilities are not
enabled (see 'CPU model features' subsection in the previous section).
Hot unplug a vfio-ap device from a running guest:
================================================
A vfio-ap device can be unplugged from a running KVM guest if a vfio-ap device
has been attached to the virtual machine's ap-bus via the QEMU command line
or a prior hot plug action.
To hot unplug a vfio-ap device, use the QEMU device_del command:
(qemu) device_del vfio-ap,sysfsdev="$path-to-mdev"
Where $path-to-mdev is the same as the path specified when the vfio-ap
device was attached to the virtual machine's ap-bus.
On a Linux guest, the AP devices will be removed from the /sys/bus/ap/devices
directory on the guest when the AP bus subsequently performs its periodic scan,
so there may be a short delay before the AP devices are no longer accessible by
the guest.
The command will fail if the $path-to-mdev specified on the device_del command
does not match the value specified when the vfio-ap device was attached to
the virtual machine's ap-bus.
Example: Configure AP Matrixes for Three Linux Guests:
=====================================================
Let's now provide an example to illustrate how KVM guests may be given
@ -819,7 +866,11 @@ Limitations
assigned lest the host be given access to the private data of the AP queue
device, such as a private key configured specifically for the guest.
* Dynamically modifying the AP matrix for a running guest (which would amount to
hot(un)plug of AP devices for the guest) is currently not supported
* Dynamically assigning AP resources to or unassigning AP resources from a
mediated matrix device - see 'Configuring an AP matrix for a linux guest'
section above - while a running guest is using it is currently not supported.
* Live guest migration is not supported for guests using AP devices.
* Live guest migration is not supported for guests using AP devices. If a guest
is using AP devices, the vfio-ap device configured for the guest must be
unplugged before migrating the guest (see 'Hot unplug a vfio-ap device from a
running guest' section above.