Re: [PATCH 5.4.y] KVM: s390: disable migration mode when dirty tracking is disabled

[Greg KH <greg@kroah.com>]

On Mon, Mar 06, 2023 at 04:13:31PM +0100, Nico Boehr wrote:
> 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>

Thanks, all backports now queued up.

greg k-h