[RESEND 2/3] powerpc/memcpy: Add memcpy_mcsafe for pmem

[Dan Williams]

[ adding Matthew, Christoph, and Tony  ]

On Wed, Apr 4, 2018 at 4:57 PM, Nicholas Piggin <npiggin at gmail.com> wrote:
> On Thu,  5 Apr 2018 09:19:42 +1000
> Balbir Singh <bsingharora at 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.