From 0aed55af88345b5d673240f90e671d79662fb01e Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Mon, 29 May 2017 12:22:50 -0700 Subject: x86, uaccess: introduce copy_from_iter_flushcache for pmem / cache-bypass operations 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_flushcache, memcpy_page_flushcache, and memcpy_flushcache, that guarantee that the destination buffer is not dirty in the cpu cache on completion. The new copy_from_iter_flushcache 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_flushcache() and memcpy_flushcache() are gated by the CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE 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]. The first consumer of this interface is a new 'copy_from_iter' dax operation so that pmem can inject cache maintenance operations without imposing this overhead on other dax-capable drivers. [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: Cc: Jan Kara Cc: Jeff Moyer Cc: Ingo Molnar Cc: Christoph Hellwig Cc: Toshi Kani Cc: "H. Peter Anvin" Cc: Al Viro Cc: Thomas Gleixner Cc: Matthew Wilcox Reviewed-by: Ross Zwisler Signed-off-by: Dan Williams --- drivers/nvdimm/region_devs.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'drivers/nvdimm/region_devs.c') diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c index b550edf2571f..985b0e11bd73 100644 --- a/drivers/nvdimm/region_devs.c +++ b/drivers/nvdimm/region_devs.c @@ -1015,8 +1015,8 @@ void nvdimm_flush(struct nd_region *nd_region) * The first wmb() is needed to 'sfence' all previous writes * such that they are architecturally visible for the platform * buffer flush. Note that we've already arranged for pmem - * writes to avoid the cache via arch_memcpy_to_pmem(). The - * final wmb() ensures ordering for the NVDIMM flush write. + * writes to avoid the cache via memcpy_flushcache(). The final + * wmb() ensures ordering for the NVDIMM flush write. */ wmb(); for (i = 0; i < nd_region->ndr_mappings; i++) -- cgit v1.2.1