Re: [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter()

[Dan Williams]

On Tue, May 1, 2018 at 7:53 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, May 1, 2018 at 7:26 PM Dan Williams <dan.j.williams@xxxxxxxxx>
> wrote:
>
>> Right, but the only way to make MCE non-fatal is to teach the machine
>> check handler about recoverable conditions. This patch teaches the
>> machine check handler how to recover copy_to_iter() errors.
>
> Why not just unmap the page and remap a new page  in its place? Meaning
> that it needs absolutely no special error handling in the callers.
>
> IOW, treat it *exactly*  like the whole page poisoning.
>
> We _have_ the technology. Why does this code think it's such a special
> snow-flake?

Because dax. There's no page cache indirection games we can play here
to poison a page and map in another page. The mapped page is 1:1
associated with the filesystem block and physical memory address.