On Wed, Apr 4, 2018 at 11:45 PM, Nicholas Piggin <npig...@gmail.com> wrote: > On Thu, 5 Apr 2018 15:53:07 +1000 > Balbir Singh <bsinghar...@gmail.com> wrote: > >> On Thu, 5 Apr 2018 15:04:05 +1000 >> Nicholas Piggin <npig...@gmail.com> wrote: >> >> > On Wed, 4 Apr 2018 20:00:52 -0700 >> > Dan Williams <dan.j.willi...@intel.com> wrote: >> > >> > > [ adding Matthew, Christoph, and Tony ] >> > > >> > > On Wed, Apr 4, 2018 at 4:57 PM, Nicholas Piggin <npig...@gmail.com> >> > > wrote: >> > > > On Thu, 5 Apr 2018 09:19:42 +1000 >> > > > Balbir Singh <bsinghar...@gmail.com> wrote: >> > > > >> > > >> The pmem infrastructure uses memcpy_mcsafe in the pmem >> > > >> layer so as to convert machine check excpetions into >> > > >> a return value on failure in case a machine check >> > > >> exception is encoutered during the memcpy. >> > > >> >> > > >> This patch largely borrows from the copyuser_power7 >> > > >> logic and does not add the VMX optimizations, largely >> > > >> to keep the patch simple. If needed those optimizations >> > > >> can be folded in. >> > > > >> > > > So memcpy_mcsafe doesn't return number of bytes copied? >> > > > Huh, well that makes it simple. >> > > >> > > Well, not in current kernels, but we need to add that support or >> > > remove the direct call to copy_to_iter() in fs/dax.c. I'm looking >> > > right now to add "bytes remaining" support to the x86 memcpy_mcsafe(), >> > > but for copy_to_user we also need to handle bytes remaining for write >> > > faults. That fix is hopefully something that can land in an early >> > > 4.17-rc, but it won't be ready for -rc1. >> > >> > I wonder if the powerpc implementation should just go straight to >> > counting bytes. Backporting to this interface would be trivial, but >> > it would just mean there's only one variant of the code to support. >> > That's up to Balbir though. >> > >> >> I'm thinking about it, I wonder what "bytes remaining" mean in pmem context >> in the context of a machine check exception. Also, do we want to be byte >> accurate or cache-line accurate for the bytes remaining? The former is much >> easier than the latter :) > > The ideal would be a linear measure of how much of your copy reached > (or can reach) non-volatile storage with nothing further copied. You > may have to allow for some relaxing of the semantics depending on > what the architecture can support. > > What's the problem with just counting bytes copied like usercopy -- > why is that harder than cacheline accuracy? > >> I'd rather implement the existing interface and port/support the new >> interface >> as it becomes available > > Fair enough.
I have patches already in progress to change the interface. My preference is to hold off on adding a new implementation that will need to be immediately reworked. When I say "immediate" I mean that should be able to post what I have for review within the next few days. Whether this is all too late for 4.17 is another question...