On Wed, Mar 17, 2021 at 04:52:03PM -0700, Dan Williams wrote: > On Wed, Mar 17, 2021 at 4:49 AM Stefan Hajnoczi <stefa...@redhat.com> wrote: > > > > Hi, > > Microsoft and Intel developed two different ACPI NVDIMM _DSM interfaces. > > > > The specs for the Intel interface are available here: > > https://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf > > > > This is the interface that QEMU emulates. It has been reported that > > Windows 2016 Server and 2019 Server guests do not recognize QEMU's > > emulated NVDIMM devices using the Microsoft driver. > > > > I'd like to understand the path forward that will allow both Linux and > > Windows guests to successfully use QEMU's emulated NVDIMM device > > (https://gitlab.com/qemu-project/qemu/-/blob/master/hw/acpi/nvdimm.c). > > > > Are/have these two interfaces being/been unified? > > No, they service 2 different classes of NVDIMMs. The Microsoft > specification was defined for NVDIMM-N devices that are the > traditional battery/super-capacitor backed DDR with sometimes an equal > amount of flash to squirrel away data to non-volatile media on power > loss. The Intel one is for a persistent media class of device where > there is no need to communicate health attributes like "energy source > died" or "restore from flash" failed. > > > Should QEMU emulate both of them to make running Windows guests easy? > > Depends on how tolerant Windows is to different format-interface-code > implementations and what QEMU should return on each of the functions > it decides to implement. > > Note that QEMU only implements a small subset of the Intel commands, > i.e. just enough to provision namespaces in the NVDIMM label area. > "NVDIMM label area" is a concept that is newer than the NVDIMM-N > definition which is why you don't see labels mentioned in the > Microsoft specification. Since then ACPI has developed common label > area access methods, see "6.5.10 NVDIMM Label Methods" in the ACPI 6.4 > specification. > > Note that you'll also see "9.20.8 NVDIMM Device Methods" in that spec > for some health management commands that overlap what the Microsoft > and Intel specs communicate. Linux does not support them since any > platform that might support them will also support the Intel > specification so there's no driving need for Linux to migrate. I do > not know the status of that command support in Windows, or the HPE > command support in Windows for that matter. > > If you need to support guests that expect the Hyper-V command > definition, and will fail to attach NVDIMM support in the absence of > that definition then QEMU needs UUID_NFIT_DIMM_N_HYPERV support, note > that is a different command set than even UUID_NFIT_DIMM_N_MSFT > (include/acpi/acuuid.h). That would also require changes to virtual > ACPI NFIT to advertise the correlated format interface code. There may > be more... you would need someone from Hyper-V land to enumerate all > that is expected. >
Thanks! Stefan
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