On 3/17/20 4:23 AM, Stefan Hajnoczi wrote: >> Code is posted here >> https://github.com/AndrzejJakowski/qemu/commit/3a7762a1d13ff1543d1da430748eb24e38faab6f >> >> QEMU command line: >> >> # below are just relevant pieces of configuration, other stuff omitted >> # tried different setting (e.g. pmem=on and pmem=off) >> >> ./x86_64-softmmu/qemu-system-x86_64 ... \ >> -object >> memory-backend-file,id=mem1,share=off,pmem=on,mem-path=../nvme_pmr.bin,size=$((1*1024*1024)) >> \ > share=off is MAP_PRIVATE. If persistence is desired then share=on > should be used. > > However, this shouldn't affect "system_reset" behavior since the QEMU > process still has the same mapped file open. >
Hi Stefan, Thx!! share=off setting was the problem. I confirmed with my simple test that persistence is achieved. I didn't find API to perform flush (msync). Any suggestion what function to use? Given that host memory backend is working I think my patch is almost ready for resubmission -- let me know if there are any other comments. Andrzej >> -drive file=../nvme.bin,format=raw,if=none,id=nvme_emulated \ >> -device nvme,drive=nvme_emulated,serial="test serial",pmrdev=mem1 >> >> In VM: >> My persisent memory region is exposed PCI BAR >> Region 2: Memory at fe000000 (64-bit, prefetchable) [size=1M] >> >> So I perform reads/writes from/to following adress 0xfe000000 (decimal >> 4261412864) >> >> dd if=test.bin of=/dev/mem bs=1 count=30 seek=4261412864 >> dd if=/dev/mem of=test1.bin bs=1 count=30 skip=4261412864 > Did you verify that the guest kernel is really accessing the BAR? I > remember that distro kernels often ship with options that make > /dev/mem of limited use because it's considered insecure. > >> On VMM I didn't observe that backing file has been updated and after power >> cycling VM >> I see old junk when reading PMR region. > Did you check that the pmrdev mmap region contains the data the guest > wrote before power cycling? > >> Also from include/qemu/pmem.h it looks like pmem_persist() will cause qemu >> to exit >> if libpmem is not installed: > The libpmem support only needs to be used when the pmem=on option was > given. If there isn't a physical pmem device then it doesn't need to > be used. > > Stefan
