On Thu, May 24, 2018 at 12:19 AM, Yasunori Goto <y-g...@jp.fujitsu.com> wrote: >> On Tue, May 22, 2018 at 10:08 PM, Yasunori Goto <y-g...@jp.fujitsu.com> >> wrote: >> > Hello, >> > >> > I'm investigating status of vNVDIMM on qemu/KVM, >> > and I have some questions about it. I'm glad if anyone answer them. >> > >> > In my understanding, qemu/KVM has a feature to show NFIT for guest, >> > and it will be still updated about platform capability with this patch set. >> > https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg04756.html >> > >> > And libvirt also supports this feature with <memory model='nvdimm'> >> > https://libvirt.org/formatdomain.html#elementsMemory >> > >> > >> > However, virtio-pmem is developing now, and it is better >> > for archtectures to detect regions of NVDIMM without ACPI (like s390x) >> >> I think you are confusing virtio-pmem (patches from Pankaj) and >> virtio-mem (patches from David)? ...or I'm confused. > > Probably, "I" am confusing. > So, your clarification is very helpful for me. > > >> >> > In addition, It is also necessary to flush guest contents on vNVDIMM >> > who has a backend-file. >> >> virtio-pmem is a mechanism to use host page cache as pmem in a guest. >> It does not support high performance memory applications because it >> requires fsync/msync. I.e. it is not DAX it is the traditional mmap >> I/O model, but moving page cache management to the host rather than >> duplicating it in guests. > > Ah, ok. > > >> >> > Q1) Does ACPI.NFIT bus of qemu/kvm remain with virtio-pmem? >> > How do each roles become it if both NFIT and virtio-pmem will be >> > available? >> > If my understanding is correct, both NFIT and virtio-pmem is used to >> > detect vNVDIMM regions, but only one seems to be necessary.... >> >> We need both because they are different. Guest DAX should not be using >> virtio-pmem. > > Hmm. Ok. > > But ,I would like understand one more thing. > In the following mail, it seems that e820 bus will be used for fake DAX. > > https://lists.01.org/pipermail/linux-nvdimm/2018-January/013926.html > > Could you tell me what is relationship between "fake DAX" in this mail > and Guest DAX? > Why e820 is necessary for this case? >
It was proposed as a starting template for writing a new nvdimm bus driver. All we need is a way to communicate both the address range and the flush interface. This could be done with a new SPA Range GUID with the NFIT, or a custom virtio-pci device that registers a special nvdimm region with this property. My preference is whichever approach minimizes the code duplication, because the pmem driver should be re-used as much as possible. _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm