Hi, This two patches are posted to introduce a new method that can distinguish cases of allocating memcache more precisely, and to elide some unnecessary cache flush. For patch-1: With a guest translation fault, we don't really need the memcache pages when only installing a new entry to the existing page table or replacing the table entry with a block entry. And with a guest permission fault, we also don't need the memcache pages for a write_fault in dirty-logging time if VMs are not configured with huge mappings. So a new method is introduced to distinguish cases of allocating memcache more precisely. For patch-2: If migration of a VM with hugepages is canceled midway, KVM will adjust the stage-2 table mappings back to block mappings. With multiple vCPUs accessing guest pages within the same 1G range, there could be numbers of translation faults to handle, and KVM will uniformly flush data cache for 1G range before handling the faults. As it will cost a long time to flush the data cache for 1G range of memory(130ms on Kunpeng 920 servers, for example), the consequent cache flush for each translation fault will finally lead to vCPU stuck for seconds or even a soft lockup. I have met both the stuck and soft lockup on Kunpeng servers with FWB not supported. When KVM need to recover the table mappings back to block mappings, as we only replace the existing page tables with a block entry and the cacheability has not been changed, the cache maintenance opreations can be skipped. Yanan Wang (2): KVM: arm64: Distinguish cases of allocating memcache more precisely KVM: arm64: Skip the cache flush when coalescing tables into a block arch/arm64/kvm/mmu.c | 37 +++++++++++++++++++++---------------- 1 file changed, 21 insertions(+), 16 deletions(-) -- 2.19.1
