Re: [PATCH RFT v2 1/4] vpda: try to fix the potential crash due to misusing __GFP_NOFAIL

[Barry Song <21cnbao@gmail.com>]

On Wed, Jul 31, 2024 at 11:58 AM Jason Wang <jasowang@redhat.com> wrote:
>
> On Wed, Jul 31, 2024 at 11:15 AM Barry Song <21cnbao@gmail.com> wrote:
> >
> > On Wed, Jul 31, 2024 at 11:10 AM Jason Wang <jasowang@redhat.com> wrote:
> > >
> > > On Wed, Jul 31, 2024 at 8:03 AM Barry Song <21cnbao@gmail.com> wrote:
> > > >
> > > > From: Barry Song <v-songbaohua@oppo.com>
> > > >
> > > > mm doesn't support non-blockable __GFP_NOFAIL allocation. Because
> > > > __GFP_NOFAIL without direct reclamation may just result in a busy
> > > > loop within non-sleepable contexts.
> > > >
> > > > static inline struct page *
> > > > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> > > >                                                 struct alloc_context *ac)
> > > > {
> > > >         ...
> > > >         /*
> > > >          * Make sure that __GFP_NOFAIL request doesn't leak out and make sure
> > > >          * we always retry
> > > >          */
> > > >         if (gfp_mask & __GFP_NOFAIL) {
> > > >                 /*
> > > >                  * All existing users of the __GFP_NOFAIL are blockable, so warn
> > > >                  * of any new users that actually require GFP_NOWAIT
> > > >                  */
> > > >                 if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))
> > > >                         goto fail;
> > > >                 ...
> > > >         }
> > > >         ...
> > > > fail:
> > > >         warn_alloc(gfp_mask, ac->nodemask,
> > > >                         "page allocation failure: order:%u", order);
> > > > got_pg:
> > > >         return page;
> > > > }
> > > >
> > > > Let's move the memory allocation out of the atomic context and use
> > > > the normal sleepable context to get pages.
> > > >
> > > > [RFT]: This has only been compile-tested; I'd prefer if the VDPA maintainers
> > > > handles it.
> > > >
> > > > Cc: "Michael S. Tsirkin" <mst@redhat.com>
> > > > Cc: Jason Wang <jasowang@redhat.com>
> > > > Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > > Cc: "Eugenio Pérez" <eperezma@redhat.com>
> > > > Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
> > > > Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> > > > ---
> > > >  drivers/vdpa/vdpa_user/iova_domain.c | 31 +++++++++++++++++++++++-----
> > > >  drivers/vdpa/vdpa_user/iova_domain.h |  5 ++++-
> > > >  drivers/vdpa/vdpa_user/vduse_dev.c   |  4 +++-
> > > >  3 files changed, 33 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c
> > > > index 791d38d6284c..9318f059a8b5 100644
> > > > --- a/drivers/vdpa/vdpa_user/iova_domain.c
> > > > +++ b/drivers/vdpa/vdpa_user/iova_domain.c
> > > > @@ -283,7 +283,23 @@ int vduse_domain_add_user_bounce_pages(struct vduse_iova_domain *domain,
> > > >         return ret;
> > > >  }
> > > >
> > > > -void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain)
> > > > +struct page **vduse_domain_alloc_pages_to_remove_bounce(struct vduse_iova_domain *domain)
> > > > +{
> > > > +       struct page **pages;
> > > > +       unsigned long count, i;
> > > > +
> > > > +       if (!domain->user_bounce_pages)
> > > > +               return NULL;
> > > > +
> > > > +       count = domain->bounce_size >> PAGE_SHIFT;
> > > > +       pages = kmalloc_array(count, sizeof(*pages), GFP_KERNEL | __GFP_NOFAIL);
> > > > +       for (i = 0; i < count; i++)
> > > > +               pages[i] = alloc_page(GFP_KERNEL | __GFP_NOFAIL);
> > > > +
> > > > +       return pages;
> > > > +}
> > > > +
> > > > +void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain, struct page **pages)
> > > >  {
> > > >         struct vduse_bounce_map *map;
> > > >         unsigned long i, count;
> > > > @@ -294,15 +310,16 @@ void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain)
> > > >
> > > >         count = domain->bounce_size >> PAGE_SHIFT;
> > > >         for (i = 0; i < count; i++) {
> > > > -               struct page *page = NULL;
> > > > +               struct page *page = pages[i];
> > > >
> > > >                 map = &domain->bounce_maps[i];
> > > > -               if (WARN_ON(!map->bounce_page))
> > > > +               if (WARN_ON(!map->bounce_page)) {
> > > > +                       put_page(page);
> > > >                         continue;
> > > > +               }
> > > >
> > > >                 /* Copy user page to kernel page if it's in use */
> > > >                 if (map->orig_phys != INVALID_PHYS_ADDR) {
> > > > -                       page = alloc_page(GFP_ATOMIC | __GFP_NOFAIL);
> > > >                         memcpy_from_page(page_address(page),
> > > >                                          map->bounce_page, 0, PAGE_SIZE);
> > > >                 }
> > > > @@ -310,6 +327,7 @@ void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain)
> > > >                 map->bounce_page = page;
> > > >         }
> > > >         domain->user_bounce_pages = false;
> > > > +       kfree(pages);
> > > >  out:
> > > >         write_unlock(&domain->bounce_lock);
> > > >  }
> > > > @@ -543,10 +561,13 @@ static int vduse_domain_mmap(struct file *file, struct vm_area_struct *vma)
> > > >  static int vduse_domain_release(struct inode *inode, struct file *file)
> > > >  {
> > > >         struct vduse_iova_domain *domain = file->private_data;
> > > > +       struct page **pages;
> > > > +
> > > > +       pages = vduse_domain_alloc_pages_to_remove_bounce(domain);
> > > >
> > > >         spin_lock(&domain->iotlb_lock);
> > > >         vduse_iotlb_del_range(domain, 0, ULLONG_MAX);
> > > > -       vduse_domain_remove_user_bounce_pages(domain);
> > > > +       vduse_domain_remove_user_bounce_pages(domain, pages);
> > > >         vduse_domain_free_kernel_bounce_pages(domain);
> > > >         spin_unlock(&domain->iotlb_lock);
> > > >         put_iova_domain(&domain->stream_iovad);
> > > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.h b/drivers/vdpa/vdpa_user/iova_domain.h
> > > > index f92f22a7267d..17efa5555b3f 100644
> > > > --- a/drivers/vdpa/vdpa_user/iova_domain.h
> > > > +++ b/drivers/vdpa/vdpa_user/iova_domain.h
> > > > @@ -74,7 +74,10 @@ void vduse_domain_reset_bounce_map(struct vduse_iova_domain *domain);
> > > >  int vduse_domain_add_user_bounce_pages(struct vduse_iova_domain *domain,
> > > >                                        struct page **pages, int count);
> > > >
> > > > -void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain);
> > > > +void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain,
> > > > +                                          struct page **pages);
> > > > +
> > > > +struct page **vduse_domain_alloc_pages_to_remove_bounce(struct vduse_iova_domain *domain);
> > > >
> > > >  void vduse_domain_destroy(struct vduse_iova_domain *domain);
> > > >
> > > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > index 7ae99691efdf..5d8d5810df57 100644
> > > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > @@ -1030,6 +1030,7 @@ static int vduse_dev_queue_irq_work(struct vduse_dev *dev,
> > > >  static int vduse_dev_dereg_umem(struct vduse_dev *dev,
> > > >                                 u64 iova, u64 size)
> > > >  {
> > > > +       struct page **pages;
> > > >         int ret;
> > > >
> > > >         mutex_lock(&dev->mem_lock);
> > > > @@ -1044,7 +1045,8 @@ static int vduse_dev_dereg_umem(struct vduse_dev *dev,
> > > >         if (dev->umem->iova != iova || size != dev->domain->bounce_size)
> > > >                 goto unlock;
> > > >
> > > > -       vduse_domain_remove_user_bounce_pages(dev->domain);
> > > > +       pages = vduse_domain_alloc_pages_to_remove_bounce(dev->domain);
> > > > +       vduse_domain_remove_user_bounce_pages(dev->domain, pages);
> > > >         unpin_user_pages_dirty_lock(dev->umem->pages,
> > > >                                     dev->umem->npages, true);
> > > >         atomic64_sub(dev->umem->npages, &dev->umem->mm->pinned_vm);
> > >
> > > We miss a kfree(pages); here?
> > no.
> > i've moved it into vduse_domain_remove_user_bounce_pages.
>
> Ok, but it seems tricky e.g allocated by the caller but freed in
> callee. And I think I missed some important issues in the previous
> review: The check of user_bounce_pages must be done under the
> bounce_lock, otherwise it might race with umem_reg.
>
> So in the case of release(), we know the device is gone, so there's no
> need to allocate pages that will be released soon. So we can pass NULL
> as a hint and just assign bounce_page to NULL in
> vduse_domain_remove_user_bounce_pages().
>
> And in the case of vduse_dev_dereg_umem(), we need to allocate the
> pages without checking user_bounce_pages. So in
> vduse_domain_remove_user_bounce_pages() if we can free the allocated
> pages as well as the pages in the following check
>
>         if (!domain->user_bounce_pages)
>                 goto out;
>
> What do you think?

I am not a vdpa guy, but  changing the current logic is another patch.
From mm perspective, I can only address the __GFP_NOFAIL issue.

I actually prefer you guys handle it  directly:-) I'd rather report a BUG
instead. TBH, I know nothing about vpda.

>
> Thanks
>
> >
> > >
> > > Thanks
> > >
> > > > --
> > > > 2.34.1
> > > >
> > >
Thanks
Barry