> On Apr 30, 2020, at 5:25 PM, Linus Torvalds <torva...@linux-foundation.org>
> wrote:
>
>
> It wasn't clear how "copy_to_mc()" could ever fault. Poisoning
> after-the-fact? Why would that be preferable to just mapping a dummy
> page?
If the kernel gets an async memory error and maps a dummy page, then subsequent
reads will subsequently succeed and return garbage when they should fail. If
x86 had write-only pages, we could map a dummy write-only page. But we don’t,
so I think we’re stuck.
As for naming the kind of memory we’re taking about, ISTM there are two
classes: DAX and monstrous memory-mapped non-persistent cache devices. Both
could be Optane, I suppose.
But I also think it’s legitimate to use these accessors to increase the chance
of surviving a failure of normal memory. If a normal page happens to be page
cache when it fails and if page cache access use these fancy accessors, then we
might actually survive a failure.
We could be ambitious: declare that all page cache and all get_user_page’d
memory should use the new accessors. I doubt we’ll ever really succeed due to
magical things like rseq and anything that thinks that users can set up their
own memory as a kernel-accessed ring buffer, but I suppose we could try.
