On 3/16/20 4:32 AM, Stefan Hajnoczi wrote: > On Wed, Mar 11, 2020 at 11:08:27PM -0700, Klaus Birkelund Jensen wrote: >> On Mar 11 15:54, Andrzej Jakowski wrote: >>> On 3/11/20 2:20 AM, Stefan Hajnoczi wrote: >>>> Please try: >>>> >>>> $ git grep pmem >>>> >>>> backends/hostmem-file.c is the backend that can be used and the >>>> pmem_persist() API can be used to flush writes. >>> I've reworked this patch into hostmem-file type of backend. >>> From simple tests in virtual machine: writing to PMR region >>> and then reading from it after VM power cycle I have observed that >>> there is no persistency. > Sounds like an integration bug. QEMU's NVDIMM emulation uses > HostMemoryBackend and file contents survive guest reboot. > > If you would like help debugging this, please post a link to the code > and the command-line that you are using. >
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)) \ -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 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. Also from include/qemu/pmem.h it looks like pmem_persist() will cause qemu to exit if libpmem is not installed: #ifndef QEMU_PMEM_H #define QEMU_PMEM_H #ifdef CONFIG_LIBPMEM #include <libpmem.h> #else /* !CONFIG_LIBPMEM */ static inline void * pmem_memcpy_persist(void *pmemdest, const void *src, size_t len) { /* If 'pmem' option is 'on', we should always have libpmem support, or qemu will report a error and exit, never come here. */ g_assert_not_reached(); return NULL; } static inline void pmem_persist(const void *addr, size_t len) { g_assert_not_reached(); } #endif /* CONFIG_LIBPMEM */ #endif /* QEMU_PMEM_H */
