On Fri, 2017-04-28 at 12:39 -0700, Dan Williams 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.ht > ml > > Cc: <x...@kernel.org> > Cc: Jan Kara <j...@suse.cz> > Cc: Jeff Moyer <jmo...@redhat.com> > Cc: Ingo Molnar <mi...@redhat.com> > Cc: Christoph Hellwig <h...@lst.de> > Cc: "H. Peter Anvin" <h...@zytor.com> > Cc: Al Viro <v...@zeniv.linux.org.uk> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Matthew Wilcox <mawil...@microsoft.com> > Cc: Ross Zwisler <ross.zwis...@linux.intel.com> > Signed-off-by: Dan Williams <dan.j.willi...@intel.com> > --- > Changes since the initial RFC: > * s/writethru/wt/ since we already have ioremap_wt(), > set_memory_wt(), etc. (Ingo)
Sorry I should have said earlier, but I think the term "wt" is misleading. Non-temporal stores used in memcpy_wt() provide WC semantics, not WT semantics. How about using "nocache" as it's been used in __copy_user_nocache()? Thanks, -Toshi
