On Mon, Apr 17, 2023 at 10:16:28AM -0300, Jason Gunthorpe wrote:
> On Mon, Apr 17, 2023 at 02:13:39PM +0100, Lorenzo Stoakes wrote:
> > On Mon, Apr 17, 2023 at 10:09:36AM -0300, Jason Gunthorpe wrote:
> > > On Sat, Apr 15, 2023 at 12:27:31AM +0100, Lorenzo Stoakes wrote:
> > > > The only instances of get_user_pages_remote() invocations which used the
> > > > vmas parameter were for a single page which can instead simply look up the
> > > > VMA directly. In particular:-
> > > >
> > > > - __update_ref_ctr() looked up the VMA but did nothing with it so we simply
> > > > remove it.
> > > >
> > > > - __access_remote_vm() was already using vma_lookup() when the original
> > > > lookup failed so by doing the lookup directly this also de-duplicates the
> > > > code.
> > > >
> > > > This forms part of a broader set of patches intended to eliminate the vmas
> > > > parameter altogether.
> > > >
> > > > Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> > > > ---
> > > > arch/arm64/kernel/mte.c | 5 +++--
> > > > arch/s390/kvm/interrupt.c | 2 +-
> > > > fs/exec.c | 2 +-
> > > > include/linux/mm.h | 2 +-
> > > > kernel/events/uprobes.c | 10 +++++-----
> > > > mm/gup.c | 12 ++++--------
> > > > mm/memory.c | 9 +++++----
> > > > mm/rmap.c | 2 +-
> > > > security/tomoyo/domain.c | 2 +-
> > > > virt/kvm/async_pf.c | 3 +--
> > > > 10 files changed, 23 insertions(+), 26 deletions(-)
> > > >
> > > > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> > > > index f5bcb0dc6267..74d8d4007dec 100644
> > > > --- a/arch/arm64/kernel/mte.c
> > > > +++ b/arch/arm64/kernel/mte.c
> > > > @@ -437,8 +437,9 @@ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
> > > > struct page *page = NULL;
> > > >
> > > > ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page,
> > > > - &vma, NULL);
> > > > - if (ret <= 0)
> > > > + NULL);
> > > > + vma = vma_lookup(mm, addr);
> > > > + if (ret <= 0 || !vma)
> > > > break;
> > >
> > > Given the slightly tricky error handling, it would make sense to turn
> > > this pattern into a helper function:
> > >
> > > page = get_single_user_page_locked(mm, addr, gup_flags, &vma);
> > > if (IS_ERR(page))
> > > [..]
> > >
> > > static inline struct page *get_single_user_page_locked(struct mm_struct *mm,
> > > unsigned long addr, int gup_flags, struct vm_area_struct **vma)
> > > {
> > > struct page *page;
> > > int ret;
> > >
> > > ret = get_user_pages_remote(*mm, addr, 1, gup_flags, &page, NULL, NULL);
> > > if (ret < 0)
> > > return ERR_PTR(ret);
> > > if (WARN_ON(ret == 0))
> > > return ERR_PTR(-EINVAL);
> > > *vma = vma_lookup(mm, addr);
> > > if (WARN_ON(!*vma) {
> > > put_user_page(page);
> > > return ERR_PTR(-EINVAL);
> > > }
> > > return page;
> > > }
> > >
> > > It could be its own patch so this change was just a mechanical removal
> > > of NULL
> > >
> > > Jason
> > >
> >
> > Agreed, I think this would work better as a follow up patch however so as
> > not to distract too much from the core change.
>
> I don't think you should open code sketchy error handling in several
> places and then clean it up later. Just do it right from the start.
>
Intent was to do smallest change possible (though through review that grew
of course), but I see your point, in this instance this is fiddly stuff and
probably better to abstract it to enforce correct handling.
I'll respin + add something like this.
> Jason
