s390x/vfio-ap: document hot plug/unplug of vfio-ap device
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>
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@ -440,8 +440,7 @@ unassign_control_domain
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'unassign_domain' file. This may be done multiple times to unassign more than
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'unassign_domain' file. This may be done multiple times to unassign more than
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one control domain.
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one control domain.
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Notes: Hot plug/unplug is not currently supported for mediated AP matrix
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Notes: No changes to the AP matrix will be allowed while a guest using
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devices, so no changes to the AP matrix will be allowed while a guest using
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the mediated matrix device is running. Attempts to assign an adapter,
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the mediated matrix device is running. Attempts to assign an adapter,
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domain or control domain will be rejected and an error (EBUSY) returned.
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domain or control domain will be rejected and an error (EBUSY) returned.
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@ -562,6 +561,54 @@ facilities:
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for guest usage, no AP devices can be made accessible to a
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for guest usage, no AP devices can be made accessible to a
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guest started without APFT installed.
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guest started without APFT installed.
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Hot plug a vfio-ap device into a running guest:
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==============================================
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Only one vfio-ap device can be attached to the virtual machine's ap-bus, so a
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vfio-ap device can be hot plugged if and only if no vfio-ap device is attached
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to the bus already, whether via the QEMU command line or a prior hot plug
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action.
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To hot plug a vfio-ap device, use the QEMU device_add command:
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(qemu) device_add vfio-ap,sysfsdev="$path-to-mdev"
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Where the '$path-to-mdev' value specifies the absolute path to a mediated
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device to which AP resources to be used by the guest have been assigned.
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Note that on Linux guests, the AP devices will be created in the
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/sys/bus/ap/devices directory when the AP bus subsequently performs its periodic
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scan, so there may be a short delay before the AP devices are accessible on the
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guest.
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The command will fail if:
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* A vfio-ap device has already been attached to the virtual machine's ap-bus.
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* The CPU model features for controlling guest access to AP facilities are not
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enabled (see 'CPU model features' subsection in the previous section).
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Hot unplug a vfio-ap device from a running guest:
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================================================
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A vfio-ap device can be unplugged from a running KVM guest if a vfio-ap device
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has been attached to the virtual machine's ap-bus via the QEMU command line
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or a prior hot plug action.
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To hot unplug a vfio-ap device, use the QEMU device_del command:
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(qemu) device_del vfio-ap,sysfsdev="$path-to-mdev"
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Where $path-to-mdev is the same as the path specified when the vfio-ap
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device was attached to the virtual machine's ap-bus.
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On a Linux guest, the AP devices will be removed from the /sys/bus/ap/devices
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directory on the guest when the AP bus subsequently performs its periodic scan,
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so there may be a short delay before the AP devices are no longer accessible by
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the guest.
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The command will fail if the $path-to-mdev specified on the device_del command
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does not match the value specified when the vfio-ap device was attached to
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the virtual machine's ap-bus.
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Example: Configure AP Matrixes for Three Linux Guests:
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Example: Configure AP Matrixes for Three Linux Guests:
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=====================================================
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=====================================================
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Let's now provide an example to illustrate how KVM guests may be given
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Let's now provide an example to illustrate how KVM guests may be given
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@ -819,7 +866,11 @@ Limitations
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assigned lest the host be given access to the private data of the AP queue
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assigned lest the host be given access to the private data of the AP queue
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device, such as a private key configured specifically for the guest.
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device, such as a private key configured specifically for the guest.
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* Dynamically modifying the AP matrix for a running guest (which would amount to
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* Dynamically assigning AP resources to or unassigning AP resources from a
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hot(un)plug of AP devices for the guest) is currently not supported
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mediated matrix device - see 'Configuring an AP matrix for a linux guest'
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section above - while a running guest is using it is currently not supported.
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* Live guest migration is not supported for guests using AP devices.
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* Live guest migration is not supported for guests using AP devices. If a guest
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is using AP devices, the vfio-ap device configured for the guest must be
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unplugged before migrating the guest (see 'Hot unplug a vfio-ap device from a
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running guest' section above.
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