Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"?

[Linus Torvalds]

On Tue, Jun 22, 2021 at 11:05 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> Huh?  Last I checked, the fault_in_readable actually read a byte from
> the page.  It has to wait for the read to complete before that can
> happen.

Yeah, we don't have any kind of async fault-in model.

I'm not sure how that would even look. I don't think it would
necessarily be *impossible* (special marker in the exception table to
let the fault code know that this is a "prepare" fault), but it would
be pretty challenging.

            Linus