2:54 a.m.
* Dan Williams <dan.j.williams(a)intel.com> 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(a)kernel.org>
Cc: Jan Kara <jack(a)suse.cz>
Cc: Jeff Moyer <jmoyer(a)redhat.com>
Cc: Ingo Molnar <mingo(a)redhat.com>
Cc: Christoph Hellwig <hch(a)lst.de>
Cc: "H. Peter Anvin" <hpa(a)zytor.com>
Cc: Al Viro <viro(a)zeniv.linux.org.uk>
Cc: Thomas Gleixner <tglx(a)linutronix.de>
Cc: Matthew Wilcox <mawilcox(a)microsoft.com>
Cc: Ross Zwisler <ross.zwisler(a)linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams(a)intel.com>
---
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(a)kernel.org>
Thanks,
Ingo