On Sat, Jun 17, 2023 at 09:00:34PM +0100, Lorenzo Stoakes wrote:
> On Sat, Jun 17, 2023 at 08:48:38PM +0100, Lorenzo Stoakes wrote:
> > On Tue, Jun 13, 2023 at 05:53:44PM -0400, Peter Xu wrote:
> > > The only path that doesn't use generic "**pages" handling is the gate vma.
> > > Make it use the same path, meanwhile tune the next_page label upper to
> > > cover "**pages" handling. This prepares for THP handling for "**pages".
> > >
> > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> > > ---
> > > mm/gup.c | 7 +++----
> > > 1 file changed, 3 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/mm/gup.c b/mm/gup.c
> > > index 8d59ae4554e7..a2d1b3c4b104 100644
> > > --- a/mm/gup.c
> > > +++ b/mm/gup.c
> > > @@ -1135,7 +1135,7 @@ static long __get_user_pages(struct mm_struct *mm,
> > > if (!vma && in_gate_area(mm, start)) {
> > > ret = get_gate_page(mm, start & PAGE_MASK,
> > > gup_flags, &vma,
> > > - pages ? &pages[i] : NULL);
> > > + pages ? &page : NULL);
> >
> > Good spot... ugh that we handled this differently.
> >
> > > if (ret)
> > > goto out;
> > > ctx.page_mask = 0;
> >
> > We can drop this line now right? As the new next_page block will duplicate
> > this.
>
> OK I can see why you left this in given the last patch in the series :)
> Please disregard.
Yes the other "page_mask=0" will be removed in the next (not last) patch.
>
> >
> > > @@ -1205,19 +1205,18 @@ static long __get_user_pages(struct mm_struct *mm,
> > > ret = PTR_ERR(page);
> > > goto out;
> > > }
> > > -
> > > - goto next_page;
> >
> > This is neat, we've already checked if pages != NULL so the if (pages)
> > block at the new next_page label will not be run.
Yes.
> >
> > > } else if (IS_ERR(page)) {
> > > ret = PTR_ERR(page);
> > > goto out;
> > > }
> > > +next_page:
> > > if (pages) {
> > > pages[i] = page;
> > > flush_anon_page(vma, page, start);
> > > flush_dcache_page(page);
> >
> > I guess there's no harm that we now flush here, though it seems to me to be
> > superfluous, it's not a big deal I don't think.
I'd say GUP on gate vma page should be so rare so yeah I think it shouldn't
be a big deal. Even iiuc vsyscall=xonly should be the default, so gup may
have already failed on a gate vma page even trying to read-only..
> >
> > > ctx.page_mask = 0;
> > > }
> > > -next_page:
> > > +
> > > page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
> > > if (page_increm > nr_pages)
> > > page_increm = nr_pages;
> > > --
> > > 2.40.1
> > >
> >
> > Other than that, LGTM,
> >
> > Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Thanks for looking!
--
Peter Xu
