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 feel like there are quite
a few things we can follow up on including assessing whether we might be
able to use _fast() paths in places (I haven't assessed this yet).
