On Fri, Feb 1, 2019 at 9:14 AM Dexuan Cui <decui@xxxxxxxxxxxxx> wrote: > > > From: Dan Williams <dan.j.williams@xxxxxxxxx> > > Sent: Tuesday, January 29, 2019 10:24 PM > > On Mon, Jan 28, 2019 at 4:56 PM Dexuan Cui <decui@xxxxxxxxxxxxx> wrote: > > > > > > > > > Add the Hyper-V _DSM command set to the white list of NVDIMM command > > > sets. > > > > > > Thanks Dan Williams <dan.j.williams@xxxxxxxxx> for writing the > > > comment change. > > > --- > > > Changes in v2: > > > Updated the comment and changelog (Thanks, Dan!) > > > Rebased to the tag libnvdimm-fixes-5.0-rc4 of the nvdimm tree. > > > > Thanks for the re-spin, applied. > > Hi Dan, > Unluckily it looks this commit causes a regression on > https://git.kernel.org/pub/scm/linux/kernel/git/djbw/nvdimm.git/log/?h=libnvdimm-pending > > With the patch, "ndctl list" shows nothing, and /dev/pmem0 can't appear. > If I revert the patch, it will be back to normal. > > I attached the config/logs. In the bad case, "dmesg" shows a line > [ 5.259017] nd_pmem namespace0.0: 0x0000000000000000, too small must be at least 0x1000 > > Any idea why this happens? I'm digging into the details and I appreciate your insights. Looks like it is working as expected. The regression you are seeing is the fact that the patch enables the kernel to enable nvdimm-namespace-label reads. Those reads find a namespace index block and a label. Unfortunately the label has the LOCAL flag set and Linux explicitly ignores pmem namespace labels with that bit set. The reason for that is due to the fact that the original definition of the LOCAL bit from v1.1 of the namespace label implementation [1] explicitly limited the LOCAL flag to "block aperture" regions. If you clear that LOCAL flag I expect it will work. To my knowledge Windows pretends that the v1.1 definition never existed. The UEFI 2.7 specification for v1.2 labels states that setting the LOCAL flag is optional when "nlabel", number of labels in the set, is 1. Linux makes that mandatory as LOCAL is redundant when nlabel is 1. That said, the Robustness Principle makes a case that Linux should tolerate the bit being set. However, it's just a non-trivial amount of work to unwind the ingrained block-aperture assumptions of that bit. [1]: http://pmem.io/documents/NVDIMM_Namespace_Spec.pdf
