Previously, when a protected VM was rebooted or when it was shut down, its memory was made unprotected, and then the protected VM itself was destroyed. Looping over the whole address space can take some time, considering the overhead of the various Ultravisor Calls (UVCs). This means that a reboot or a shutdown would take a potentially long amount of time, depending on the amount of used memory. This patchseries implements a deferred destroy mechanism for protected guests. When a protected guest is destroyed, its memory is cleared in background, allowing the guest to restart or terminate significantly faster than before. There are 2 possibilities when a protected VM is torn down: * it still has an address space associated (reboot case) * it does not have an address space anymore (shutdown case) For the reboot case, the reference count of the mm is increased, and then a background thread is started to clean up. Once the thread went through the whole address space, the protected VM is actually destroyed. For the shutdown case, a list of pages to be destroyed is formed when the mm is torn down. Instead of just unmapping the pages when the address space is being torn down, they are also set aside. Later when KVM cleans up the VM, a thread is started to clean up the pages from the list. This means that the same address space can have memory belonging to more than one protected guest, although only one will be running, the others will in fact not even have any CPUs. When a guest is destroyed, its memory still counts towards its memory control group until it's actually freed (I tested this experimentally) When the system runs out of memory, if a guest has terminated and its memory is being cleaned asynchronously, the OOM killer will wait a little and then see if memory has been freed. This has the practical effect of slowing down memory allocations when the system is out of memory to give the cleanup thread time to cleanup and free memory, and avoid an actual OOM situation. v1->v2 * rebased on a more recent kernel * improved/expanded some patch descriptions * improves/expanded some comments * added patch 1, which prevents stall notification when the system is under heavy load. * rename some members of struct deferred_priv to improve readability * avoid an use-after-free bug of the struct mm in case of shutdown * add missing return when lazy destroy is disabled * add support for OOM notifier Claudio Imbrenda (13): KVM: s390: pv: avoid stall notifications for some UVCs KVM: s390: pv: leak the ASCE page when destroy fails KVM: s390: pv: properly handle page flags for protected guests KVM: s390: pv: handle secure storage violations for protected guests KVM: s390: pv: handle secure storage exceptions for normal guests KVM: s390: pv: refactor s390_reset_acc KVM: s390: pv: usage counter instead of flag KVM: s390: pv: add export before import KVM: s390: pv: lazy destroy for reboot KVM: s390: pv: extend lazy destroy to handle shutdown KVM: s390: pv: module parameter to fence lazy destroy KVM: s390: pv: add OOM notifier for lazy destroy KVM: s390: pv: add support for UV feature bits arch/s390/include/asm/gmap.h | 5 +- arch/s390/include/asm/mmu.h | 3 + arch/s390/include/asm/mmu_context.h | 2 + arch/s390/include/asm/pgtable.h | 16 +- arch/s390/include/asm/uv.h | 26 ++- arch/s390/kernel/uv.c | 144 ++++++++++++++- arch/s390/kvm/kvm-s390.c | 6 +- arch/s390/kvm/kvm-s390.h | 2 +- arch/s390/kvm/pv.c | 272 ++++++++++++++++++++++++++-- arch/s390/mm/fault.c | 22 ++- arch/s390/mm/gmap.c | 86 ++++++--- 11 files changed, 530 insertions(+), 54 deletions(-) -- 2.31.1
