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From: Dan Williams <dan.j.williams@intel.com>
Date: Wed, 4 Apr 2018 20:00:52 -0700
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Subject: Re: [RESEND 2/3] powerpc/memcpy: Add memcpy_mcsafe for pmem
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To: Nicholas Piggin <npiggin@gmail.com>
Cc: "Luck, Tony" <tony.luck@intel.com>, Matthew Wilcox <mawilcox@microsoft.com>, Michael Ellerman <mpe@ellerman.id.au>, linux-nvdimm <linux-nvdimm@lists.01.org>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, Christoph Hellwig <hch@lst.de>
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[ adding Matthew, Christoph, and Tony  ]

On Wed, Apr 4, 2018 at 4:57 PM, Nicholas Piggin <npiggin@gmail.com> wrote:
> On Thu,  5 Apr 2018 09:19:42 +1000
> Balbir Singh <bsingharora@gmail.com> wrote:
>
>> The pmem infrastructure uses memcpy_mcsafe in the pmem
>> layer so as to convert machine check excpetions into
>> a return value on failure in case a machine check
>> exception is encoutered during the memcpy.
>>
>> This patch largely borrows from the copyuser_power7
>> logic and does not add the VMX optimizations, largely
>> to keep the patch simple. If needed those optimizations
>> can be folded in.
>
> So memcpy_mcsafe doesn't return number of bytes copied?
> Huh, well that makes it simple.

Well, not in current kernels, but we need to add that support or
remove the direct call to copy_to_iter() in fs/dax.c. I'm looking
right now to add "bytes remaining" support to the x86 memcpy_mcsafe(),
but for copy_to_user we also need to handle bytes remaining for write
faults. That fix is hopefully something that can land in an early
4.17-rc, but it won't be ready for -rc1.
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