Re: [PATCH 1/5] mm: Introduce mm_struct.has_pinned

From: Jann Horn
Date: Mon Sep 21 2020 - 17:44:09 EST

On Mon, Sep 21, 2020 at 11:17 PM Peter Xu <peterx@xxxxxxxxxx> wrote:
> (Commit message collected from Jason Gunthorpe)
> Reduce the chance of false positive from page_maybe_dma_pinned() by keeping
> track if the mm_struct has ever been used with pin_user_pages(). mm_structs
> that have never been passed to pin_user_pages() cannot have a positive
> page_maybe_dma_pinned() by definition.

There are some caveats here, right? E.g. this isn't necessarily true
for pagecache pages, I think?