On Wed, Apr 11, 2018 at 9:06 AM, Jeff Moyer <[email protected]> wrote: > Christoph Hellwig <[email protected]> writes: > >> On Fri, Apr 06, 2018 at 03:41:39PM -0700, Dan Williams wrote: >>> Yes, but the trust interface definition is what is missing, especially >>> when we consider memmap=ss!nn and qemu-kvm. For example do we turn off >>> DAX and/or MAP_SYNC on all platforms that don't provide a positive "I >>> have ADR" indication (ACPI 6.2 Section 5.2.25.9 NFIT Platform >>> Capabilities Structure)? >> >> Sounds like a default. > > Which do you turn off? DAX or MAP_SYNC (or both)?
Only MAP_SYNC I would say, because then userspace can't opt out of fsync/msync and it gives us a chance to "Do The Right Thing (TM)" with respect to WPQ flush. > Systems that support ACPI versions earlier than 6.2 could provide > flush hint addresses. In that case, we could assume no ADR, and turn > off MAP_SYNC, but still allow DAX. Note that I'm not aware of any > hardware that actually falls into this category. > > Platforms prior to 6.2 that don't support flush hints are currently > assumed to implement ADR. This proposal would change that default. > >>> Require opt-in when the user has trust in the hardware config that >>> the kernel can't verify? >> >> And that sounds like a good config nob ontop of that default. > > Well, we could also make a white-list for known good platforms. I > assume HPE's systems would be on that list. Otherwise we'd have to cook > up udev rules, I guess? udev rules sound good. We can distribute them in the ndctl package. I think I would handle this by making /sys/bus/nd/devices/regionX/persistence_domain writable to opt-in to a user specified persistence_domain. If the persistence_domain attribute file is not writable then you know you're on a kernel that blindly trusts all pmem descriptions as MAP_SYNC capable. > Dan, is this something you're working on now? No, it's behind finalizing dax-dma-vs-truncate and memcpy_mcsafe for user copies in my queue... _______________________________________________ Linux-nvdimm mailing list [email protected] https://lists.01.org/mailman/listinfo/linux-nvdimm
