On Apr 30, 2020, at 5:25 PM, Linus Torvalds
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
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
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.