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Date: Tue, 11 Apr 2017 09:49:13 -0600
From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-nvdimm@ml01.01.org, Jan Kara <jack@suse.cz>,
        Toshi Kani <toshi.kani@hpe.com>,
        Matthew Wilcox <mawilcox@microsoft.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Christoph Hellwig <hch@lst.de>, Jeff Moyer <jmoyer@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ross Zwisler <ross.zwisler@linux.intel.com>
Subject: Re: [PATCH v3] x86, pmem: fix broken __copy_user_nocache
 cache-bypass assumptions
Message-ID: <20170411154913.GA20725@linux.intel.com>
References: <149187075199.40875.9829505688202257056.stgit@dwillia2-desk3.amr.corp.intel.com>
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On Mon, Apr 10, 2017 at 05:35:02PM -0700, Dan Williams wrote:
> Before we rework the "pmem api" to stop abusing __copy_user_nocache()
> for memcpy_to_pmem() we need to fix cases where we may strand dirty data
> in the cpu cache. The problem occurs when copy_from_iter_pmem() is used
> for arbitrary data transfers from userspace. There is no guarantee that
> these transfers, performed by dax_iomap_actor(), will have aligned
> destinations or aligned transfer lengths. Backstop the usage
> __copy_user_nocache() with explicit cache management in these unaligned
> cases.
> 
> Yes, copy_from_iter_pmem() is now too big for an inline, but addressing
> that is saved for a later patch that moves the entirety of the "pmem
> api" into the pmem driver directly.
> 
> Fixes: 5de490daec8b ("pmem: add copy_from_iter_pmem() and clear_pmem()")
> Cc: <stable@vger.kernel.org>
> 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: Toshi Kani <toshi.kani@hpe.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

This looks good to me, thanks for fixing this.

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>