8dcdbe50ed
- kvm-scsi-generalize-scsi_SG_IO_FROM_DEV-to-scsi_SG_IO.patch [RHEL-149396] - kvm-scsi-add-error-reporting-to-scsi_SG_IO.patch [RHEL-149396] - kvm-scsi-track-SCSI-reservation-state-for-live-migration.patch [RHEL-149396] - kvm-scsi-save-load-SCSI-reservation-state.patch [RHEL-149396] - kvm-docs-add-SCSI-migrate-pr-documentation.patch [RHEL-149396] - Resolves: RHEL-149396 (Migrate SCSI PR state and preempt reservation upon live migration [rhel-9])
123 lines
4.8 KiB
Diff
123 lines
4.8 KiB
Diff
From 567a4e1af5d53804269a1fabc0b49e3ebad94648 Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Thu, 29 Jan 2026 16:20:35 -0500
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Subject: [PATCH 5/5] docs: add SCSI migrate-pr documentation
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RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
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RH-MergeRequest: 466: scsi: persistent reservation live migration
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RH-Jira: RHEL-149396
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Commit: [5/5] 96c9ada05f37484cd792c729b6bafd9ed1c71684 (stefanha/centos-stream-qemu-kvm)
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Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
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Message-id: 20260129212035.219676-6-stefanha@redhat.com
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit a67819adb2212977360e9290bd005badb07dd2e4)
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Conflicts:
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- docs/system/device-emulation.rst
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Context conflict.
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---
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docs/system/device-emulation.rst | 1 +
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docs/system/devices/scsi/index.rst | 10 +++++
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docs/system/devices/scsi/migrate-pr.rst | 54 +++++++++++++++++++++++++
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3 files changed, 65 insertions(+)
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create mode 100644 docs/system/devices/scsi/index.rst
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create mode 100644 docs/system/devices/scsi/migrate-pr.rst
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diff --git a/docs/system/device-emulation.rst b/docs/system/device-emulation.rst
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index 911381643f..72a9dbd54d 100644
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--- a/docs/system/device-emulation.rst
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+++ b/docs/system/device-emulation.rst
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@@ -91,6 +91,7 @@ Emulated Devices
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devices/keyboard.rst
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devices/net.rst
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devices/nvme.rst
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+ devices/scsi/index.rst
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devices/usb.rst
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devices/vhost-user.rst
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devices/virtio-gpu.rst
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diff --git a/docs/system/devices/scsi/index.rst b/docs/system/devices/scsi/index.rst
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new file mode 100644
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index 0000000000..4f0929b0ca
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--- /dev/null
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+++ b/docs/system/devices/scsi/index.rst
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@@ -0,0 +1,10 @@
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+SCSI Devices
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+============
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+
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+Several SCSI devices are available in QEMU. They are primarily used for block
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+storage.
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+
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+.. toctree::
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+ :maxdepth: 1
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+
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+ migrate-pr.rst
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diff --git a/docs/system/devices/scsi/migrate-pr.rst b/docs/system/devices/scsi/migrate-pr.rst
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new file mode 100644
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index 0000000000..a8f2790a86
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--- /dev/null
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+++ b/docs/system/devices/scsi/migrate-pr.rst
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@@ -0,0 +1,54 @@
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+..
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+ SPDX-License-Identifier: GPL-2.0-or-later
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+
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+.. _scsi_migrate_pr:
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+
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+SCSI Persistent Reservation Live Migration
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+==========================================
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+
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+This document explains how to live migrate SCSI Persistent Reservations.
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+
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+The ``scsi-block`` device migrates SCSI Persistent Reservations when the
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+``migrate-pr=on`` parameter is given. Migration is enabled by default in
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+versioned machine types since QEMU 11.0. It is disabled by default on older
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+machine types and needs to be explicitly enabled with ``--device
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+scsi-block,migrate-pr=on,...``.
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+
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+When migration is enabled, QEMU snoops PERSISTENT RESERVATION OUT commands and
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+tracks the reservation key registered by the guest as well as reservations that
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+the guest acquires. This information is migrated along with the guest and the
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+destination QEMU submits a PERSISTENT RESERVATION OUT command with the PREEMPT
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+service action to atomically transfer the reservation to the destination before
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+the guest starts running on the destination.
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+
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+The following persistent reservation capabilities reported by the PERSISTENT
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+RESERVATION IN command with the REPORT CAPABILITIES service action are masked
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+from the guest by QEMU when migration is enabled:
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+
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+ * Specify Initiator Ports Capable (SIP_C)
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+ * All Target Ports Capable (ATC_C)
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+
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+When migration is disabled, the ``scsi-block`` device is live migrated but
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+reservations remain in place on the source. Usually this is not the intended
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+behavior unless there is another mechanism to update reservations during
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+migration. The PERSISTENT RESERVATION IN command also does not mask
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+capabilities reported to the guest when migration is disabled.
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+
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+Limitations
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+-----------
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+
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+QEMU does not remember snooped reservation details across restart, so software
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+inside the guest must acquire the reservation after boot in order for live
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+migration to work. Similarly, if the reservation is acquired outside the guest
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+then it will not live migrate along with the guest.
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+
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+Snooping only considers the PERSISTENT RESERVATION OUT commands from the guest
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+and does not track reservation changes made by other SCSI initiators. QEMU's
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+snooped reservation details can become stale if another SCSI initiator
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+makes changes to the reservation.
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+
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+Guests running on the same host share a single SCSI initiator identity unless
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+Fibre Channel N_Port ID Virtualization is configured. As a consequence,
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+multiple guests on the same hosts may observe unexpected behavior if they use
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+the same physical LUN. From the LUN's perspective all guests are the same
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+initiator and there is no way to distinguish between guests.
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--
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2.52.0
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