Migration mode is a VM attribute which enables tracking of changes in storage attributes (PGSTE). It assumes dirty tracking is enabled on all memslots to keep a dirty bitmap of pages with changed storage attributes.
When enabling migration mode, we currently check that dirty tracking is enabled for all memslots. However, userspace can disable dirty tracking without disabling migration mode.
Since migration mode is pointless with dirty tracking disabled, disable migration mode whenever userspace disables dirty tracking on any slot.
Also update the documentation to clarify that dirty tracking must be enabled when enabling migration mode, which is already enforced by the code in kvm_s390_vm_start_migration().
Also highlight in the documentation for KVM_S390_GET_CMMA_BITS that it can now fail with -EINVAL when dirty tracking is disabled while migration mode is on. Move all the error codes to a table so this stays readable.
To disable migration mode, slots_lock should be held, which is taken in kvm_set_memory_region() and thus held in kvm_arch_prepare_memory_region().
Restructure the prepare code a bit so all the sanity checking is done before disabling migration mode. This ensures migration mode isn't disabled when some sanity check fails.
Cc: stable@vger.kernel.org Fixes: 190df4a212a7 ("KVM: s390: CMMA tracking, ESSA emulation, migration mode") Signed-off-by: Nico Boehr nrb@linux.ibm.com Reviewed-by: Janosch Frank frankja@linux.ibm.com Reviewed-by: Claudio Imbrenda imbrenda@linux.ibm.com Link: https://lore.kernel.org/r/20230127140532.230651-2-nrb@linux.ibm.com Message-Id: 20230127140532.230651-2-nrb@linux.ibm.com [frankja@linux.ibm.com: fixed commit message typo, moved api.rst error table upwards] Signed-off-by: Janosch Frank frankja@linux.ibm.com (cherry picked from commit f2d3155e2a6bac44d16f04415a321e8707d895c6) Signed-off-by: Nico Boehr nrb@linux.ibm.com --- Documentation/virt/kvm/api.rst | 18 ++++++++++++------ Documentation/virt/kvm/devices/vm.rst | 4 ++++ arch/s390/kvm/kvm-s390.c | 17 +++++++++++++++++ 3 files changed, 33 insertions(+), 6 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index b550f43214c7..ec38299f9428 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -4117,6 +4117,18 @@ not holding a previously reported uncorrected error). :Parameters: struct kvm_s390_cmma_log (in, out) :Returns: 0 on success, a negative value on error
+Errors: + + ====== ============================================================= + ENOMEM not enough memory can be allocated to complete the task + ENXIO if CMMA is not enabled + EINVAL if KVM_S390_CMMA_PEEK is not set but migration mode was not enabled + EINVAL if KVM_S390_CMMA_PEEK is not set but dirty tracking has been + disabled (and thus migration mode was automatically disabled) + EFAULT if the userspace address is invalid or if no page table is + present for the addresses (e.g. when using hugepages). + ====== ============================================================= + This ioctl is used to get the values of the CMMA bits on the s390 architecture. It is meant to be used in two scenarios:
@@ -4197,12 +4209,6 @@ mask is unused.
values points to the userspace buffer where the result will be stored.
-This ioctl can fail with -ENOMEM if not enough memory can be allocated to -complete the task, with -ENXIO if CMMA is not enabled, with -EINVAL if -KVM_S390_CMMA_PEEK is not set but migration mode was not enabled, with --EFAULT if the userspace address is invalid or if no page table is -present for the addresses (e.g. when using hugepages). - 4.108 KVM_S390_SET_CMMA_BITS ----------------------------
diff --git a/Documentation/virt/kvm/devices/vm.rst b/Documentation/virt/kvm/devices/vm.rst index 60acc39e0e93..147efec626e5 100644 --- a/Documentation/virt/kvm/devices/vm.rst +++ b/Documentation/virt/kvm/devices/vm.rst @@ -302,6 +302,10 @@ Allows userspace to start migration mode, needed for PGSTE migration. Setting this attribute when migration mode is already active will have no effects.
+Dirty tracking must be enabled on all memslots, else -EINVAL is returned. When +dirty tracking is disabled on any memslot, migration mode is automatically +stopped. + :Parameters: none :Returns: -ENOMEM if there is not enough free memory to start migration mode; -EINVAL if the state of the VM is invalid (e.g. no memory defined); diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index c61533e1448a..d7aa442ceaf1 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -5066,6 +5066,23 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, /* When we are protected, we should not change the memory slots */ if (kvm_s390_pv_get_handle(kvm)) return -EINVAL; + + if (!kvm->arch.migration_mode) + return 0; + + /* + * Turn off migration mode when: + * - userspace creates a new memslot with dirty logging off, + * - userspace modifies an existing memslot (MOVE or FLAGS_ONLY) and + * dirty logging is turned off. + * Migration mode expects dirty page logging being enabled to store + * its dirty bitmap. + */ + if (change != KVM_MR_DELETE && + !(mem->flags & KVM_MEM_LOG_DIRTY_PAGES)) + WARN(kvm_s390_vm_stop_migration(kvm), + "Failed to stop migration mode"); + return 0; }