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    SubjectRe: [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe()
    On Thu, Apr 30, 2020 at 12:50:40PM -0700, Linus Torvalds wrote:

    I see your point about the namimg being important. I think Dan's
    case is indeed "copy from pmem to user" where only options for faulting
    are #MC on the source addresses, and #PF on the destination.

    > The only *fundamental* access would likely be a single read/write
    > operation, not a copy operation. Think "get_user()" instead of
    > "copy_from_user()". Even there you get combinatorial explosions with
    > access sizes, but you can often generate those automatically or with
    > simple patterns, and then you can build up the copy functions from
    > that if you really need to.

    That's maybe very clean. But it looks like it would be hard to build
    a high performance interface on top of that primitive. Remember that
    for Dan's copy 99.999999999367673%[1] of copies will not hit a machine
    check on the read from pmem.

    Dan wants (whatever the function name) to get to a "REP MOVS" with an
    exception table entry to handle the cases where there is a fault.

    -Tony

    [1] Likely several more '9's in there

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