v2: make inter_dimm_gap a boolean and inster gap in 1 byte instead of 2Mb, due to alignment that gap would be extended up to natural backend alignment value.
it's a simplier way suggested by Michael S. Tsirkin to workaround virtio bug reported earlier: http://lists.nongnu.org/archive/html/qemu-devel/2015-08/msg00522.html where virtio can't handle buffer that crosses border between 2 DIMM's (i.e. 2 MemoryRegions). idea is to leave gaps between DIMMs, making their GPAs non contiguous, which effectively forces kmalloc to not use DIMM if buffer doesn't fit inside of it. Simpler reproducer: qemu-system-x86_64 -enable-kvm -m 256,slots=250,maxmem=32G -drive if=virtio,file=/dev/slow/rhel72 \ `for i in $(seq 0 58); do echo -n "-object memory-backend-ram,id=m$i,size=10M -device pc-dimm,id=dimm$i,memdev=m$i "; done` \ -nodefaults -snapshot -serial stdio -nographic -M pc-i440fx-2.4 if guest manages to boot just login and do: dd if=/dev/vda of=/dev/null bs=128M it will crash QEMU in 99% cases with following message: qemu-system-x86_64: virtio: error trying to map MMIO memory Igor Mammedov (2): memhp: extend address auto assignment to support gaps pc: memhp: force gaps between DIMM's GPA hw/i386/pc.c | 4 +++- hw/i386/pc_piix.c | 3 +++ hw/i386/pc_q35.c | 3 +++ hw/mem/pc-dimm.c | 13 +++++++------ hw/ppc/spapr.c | 2 +- include/hw/i386/pc.h | 1 + include/hw/mem/pc-dimm.h | 7 ++++--- 7 files changed, 22 insertions(+), 11 deletions(-) -- 1.8.3.1