* Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > The pmem driver has a need to transfer data with a persistent memory > destination and be able to rely on the fact that the destination writes > are not cached. It is sufficient for the writes to be flushed to a > cpu-store-buffer (non-temporal / "movnt" in x86 terms), as we expect > userspace to call fsync() to ensure data-writes have reached a > power-fail-safe zone in the platform. The fsync() triggers a REQ_FUA or > REQ_FLUSH to the pmem driver which will turn around and fence previous > writes with an "sfence". > > Implement a __copy_from_user_inatomic_wt, memcpy_page_wt, and memcpy_wt, > that guarantee that the destination buffer is not dirty in the cpu cache > on completion. The new copy_from_iter_wt and sub-routines will be used > to replace the "pmem api" (include/linux/pmem.h + > arch/x86/include/asm/pmem.h). The availability of copy_from_iter_wt() > and memcpy_wt() are gated by the CONFIG_ARCH_HAS_UACCESS_WT config > symbol, and fallback to copy_from_iter_nocache() and plain memcpy() > otherwise. > > This is meant to satisfy the concern from Linus that if a driver wants > to do something beyond the normal nocache semantics it should be > something private to that driver [1], and Al's concern that anything > uaccess related belongs with the rest of the uaccess code [2]. > > [1]: https://lists.01.org/pipermail/linux-nvdimm/2017-January/008364.html > [2]: https://lists.01.org/pipermail/linux-nvdimm/2017-April/009942.html > > Cc: <x86@xxxxxxxxxx> > Cc: Jan Kara <jack@xxxxxxx> > Cc: Jeff Moyer <jmoyer@xxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxx> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx> > Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > --- > Changes since the initial RFC: > * s/writethru/wt/ since we already have ioremap_wt(), set_memory_wt(), > etc. (Ingo) Looks good to me. I suspect you'd like to carry this in the nvdimm tree? Acked-by: Ingo Molnar <mingo@xxxxxxxxxx> Thanks, Ingo
