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

Nadav Amit
2021-06-22T18:16:10Z

> On Jun 22, 2021, at 11:07 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> On Tue, Jun 22, 2021 at 11:05 AM Matthew Wilcox <willy@infradead.org> 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.

I did send an RFC some time ago for “prepare” fault, but it the RFC
requires some more work.