From: "Kani, Toshimitsu" <toshi.kani@hpe.com>
To: "dan.j.williams@intel.com" <dan.j.williams@intel.com>,
"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"jmoyer@redhat.com" <jmoyer@redhat.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"hch@lst.de" <hch@lst.de>, "x86@kernel.org" <x86@kernel.org>,
"mawilcox@microsoft.com" <mawilcox@microsoft.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"ross.zwisler@linux.intel.com" <ross.zwisler@linux.intel.com>,
"jack@suse.cz" <jack@suse.cz>
Subject: Re: [PATCH v2] x86, uaccess: introduce copy_from_iter_wt for pmem / writethrough operations
Date: Fri, 5 May 2017 20:39:40 +0000 [thread overview]
Message-ID: <1494016773.30303.69.camel@hpe.com> (raw)
In-Reply-To: <149340820800.28724.16189291963486607562.stgit@dwillia2-desk3.amr.corp.intel.com>
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: <x86@kernel.org>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Jeff Moyer <jmoyer@redhat.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Matthew Wilcox <mawilcox@microsoft.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@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
next prev parent reply other threads:[~2017-05-05 20:39 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170425012230.GX29622@ZenIV.linux.org.uk>
2017-04-26 21:56 ` [RFC PATCH] x86, uaccess, pmem: introduce copy_from_iter_writethru for dax + pmem Dan Williams
2017-04-27 6:30 ` Ingo Molnar
2017-04-28 19:39 ` [PATCH v2] x86, uaccess: introduce copy_from_iter_wt for pmem / writethrough operations Dan Williams
2017-05-05 6:54 ` Ingo Molnar
2017-05-05 14:12 ` Dan Williams
2017-05-05 20:39 ` Kani, Toshimitsu [this message]
2017-05-05 22:25 ` Dan Williams
2017-05-05 22:44 ` Kani, Toshimitsu
2017-05-06 2:15 ` Dan Williams
2017-05-06 3:17 ` Kani, Toshimitsu
2017-05-06 9:46 ` Ingo Molnar
2017-05-06 13:57 ` Dan Williams
2017-05-07 8:57 ` Ingo Molnar
2017-05-08 3:01 ` Kani, Toshimitsu
2017-05-08 20:32 ` Ross Zwisler
2017-05-08 20:40 ` Dan Williams
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