Re: [RFC PATCH RESEND 06/28] mm: mark VMA as locked whenever vma->vm_flags are modified

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Sep 6, 2022 at 1:00 PM Liam Howlett <liam.howlett@oracle.com> wrote:
>
> * Suren Baghdasaryan <surenb@google.com> [220906 15:01]:
> > On Tue, Sep 6, 2022 at 7:27 AM Laurent Dufour <ldufour@linux.ibm.com> wrote:
> > >
> > > Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit :
> > > > VMA flag modifications should be done under VMA lock to prevent concurrent
> > > > page fault handling in that area.
> > > >
> > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > > ---
> > > >  fs/proc/task_mmu.c | 1 +
> > > >  fs/userfaultfd.c   | 6 ++++++
> > > >  mm/madvise.c       | 1 +
> > > >  mm/mlock.c         | 2 ++
> > > >  mm/mmap.c          | 1 +
> > > >  mm/mprotect.c      | 1 +
> > > >  6 files changed, 12 insertions(+)
> > >
> > > There are few changes also done in the driver's space, for instance:
> > >
> > > *** arch/x86/kernel/cpu/sgx/driver.c:
> > > sgx_mmap[98]                   vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND |
> > > VM_DONTDUMP | VM_IO;
> > > *** arch/x86/kernel/cpu/sgx/virt.c:
> > > sgx_vepc_mmap[108]             vma->vm_flags |= VM_PFNMAP | VM_IO |
> > > VM_DONTDUMP | VM_DONTCOPY;
> > > *** drivers/dax/device.c:
> > > dax_mmap[311]                  vma->vm_flags |= VM_HUGEPAGE;
> > >
> > > I guess these changes to vm_flags should be protected as well, or to be
> > > checked one by one.
> >
> > Thanks for noting these! I'll add necessary locking here and will look
> > for other places I might have missed.
>
> Would an inline set/clear bit function be worth while for vm_flags?  If
> it is then a name change to vm_flags may get the compiler to catch any
> missed cases.  There doesn't seem to be many cases (12 inserts) so maybe
> not.

That would probably simplify the maintenance for flags in the future
and we can add vma_mark_locked directly in the set/clear functions.

>
> >
> > >
> > > >
> > > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > > > index 4e0023643f8b..ceffa5c2c650 100644
> > > > --- a/fs/proc/task_mmu.c
> > > > +++ b/fs/proc/task_mmu.c
> > > > @@ -1285,6 +1285,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
> > > >                       for (vma = mm->mmap; vma; vma = vma->vm_next) {
> > > >                               if (!(vma->vm_flags & VM_SOFTDIRTY))
> > > >                                       continue;
> > > > +                             vma_mark_locked(vma);
> > > >                               vma->vm_flags &= ~VM_SOFTDIRTY;
> > > >                               vma_set_page_prot(vma);
> > > >                       }
> > > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> > > > index 175de70e3adf..fe557b3d1c07 100644
> > > > --- a/fs/userfaultfd.c
> > > > +++ b/fs/userfaultfd.c
> > > > @@ -620,6 +620,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
> > > >               mmap_write_lock(mm);
> > > >               for (vma = mm->mmap; vma; vma = vma->vm_next)
> > > >                       if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
> > > > +                             vma_mark_locked(vma);
> > > >                               vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > > >                               vma->vm_flags &= ~__VM_UFFD_FLAGS;
> > > >                       }
> > > > @@ -653,6 +654,7 @@ int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
> > > >
> > > >       octx = vma->vm_userfaultfd_ctx.ctx;
> > > >       if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
> > > > +             vma_mark_locked(vma);
> > > >               vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > > >               vma->vm_flags &= ~__VM_UFFD_FLAGS;
> > > >               return 0;
> > > > @@ -734,6 +736,7 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
> > > >               atomic_inc(&ctx->mmap_changing);
> > > >       } else {
> > > >               /* Drop uffd context if remap feature not enabled */
> > > > +             vma_mark_locked(vma);
> > > >               vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > > >               vma->vm_flags &= ~__VM_UFFD_FLAGS;
> > > >       }
> > > > @@ -891,6 +894,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
> > > >                       vma = prev;
> > > >               else
> > > >                       prev = vma;
> > > > +             vma_mark_locked(vma);
> > > >               vma->vm_flags = new_flags;
> > > >               vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > > >       }
> > > > @@ -1449,6 +1453,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > > >                * the next vma was merged into the current one and
> > > >                * the current one has not been updated yet.
> > > >                */
> > > > +             vma_mark_locked(vma);
> > > >               vma->vm_flags = new_flags;
> > > >               vma->vm_userfaultfd_ctx.ctx = ctx;
> > > >
> > > > @@ -1630,6 +1635,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> > > >                * the next vma was merged into the current one and
> > > >                * the current one has not been updated yet.
> > > >                */
> > > > +             vma_mark_locked(vma);
> > > >               vma->vm_flags = new_flags;
> > > >               vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > > >
> > > > diff --git a/mm/madvise.c b/mm/madvise.c
> > > > index 5f0f0948a50e..a173f0025abd 100644
> > > > --- a/mm/madvise.c
> > > > +++ b/mm/madvise.c
> > > > @@ -181,6 +181,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
> > > >       /*
> > > >        * vm_flags is protected by the mmap_lock held in write mode.
> > > >        */
> > > > +     vma_mark_locked(vma);
> > > >       vma->vm_flags = new_flags;
> > > >       if (!vma->vm_file) {
> > > >               error = replace_anon_vma_name(vma, anon_name);
> > > > diff --git a/mm/mlock.c b/mm/mlock.c
> > > > index b14e929084cc..f62e1a4d05f2 100644
> > > > --- a/mm/mlock.c
> > > > +++ b/mm/mlock.c
> > > > @@ -380,6 +380,7 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
> > > >        */
> > > >       if (newflags & VM_LOCKED)
> > > >               newflags |= VM_IO;
> > > > +     vma_mark_locked(vma);
> > > >       WRITE_ONCE(vma->vm_flags, newflags);
> > > >
> > > >       lru_add_drain();
> > > > @@ -456,6 +457,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
> > > >
> > > >       if ((newflags & VM_LOCKED) && (oldflags & VM_LOCKED)) {
> > > >               /* No work to do, and mlocking twice would be wrong */
> > > > +             vma_mark_locked(vma);
> > > >               vma->vm_flags = newflags;
> > > >       } else {
> > > >               mlock_vma_pages_range(vma, start, end, newflags);
> > > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > > index 693e6776be39..f89c9b058105 100644
> > > > --- a/mm/mmap.c
> > > > +++ b/mm/mmap.c
> > > > @@ -1818,6 +1818,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> > > >  out:
> > > >       perf_event_mmap(vma);
> > > >
> > > > +     vma_mark_locked(vma);
> > > >       vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
> > > >       if (vm_flags & VM_LOCKED) {
> > > >               if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
> > >
> > > I guess, this doesn't really impact, but the call to vma_mark_locked(vma)
> > > may be done only in the case the vm_flags field is touched.
> > > Something like this:
> > >
> > >         vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
> > >         if (vm_flags & VM_LOCKED) {
> > >                 if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
> > >                                         is_vm_hugetlb_page(vma) ||
> > > -                                       vma == get_gate_vma(current->mm))
> > > +                                       vma == get_gate_vma(current->mm)) {
> > > +                       vma_mark_locked(vma);
> > >                         vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
> > > -               else
> > > +               } else
> > >                         mm->locked_vm += (len >> PAGE_SHIFT);
> > >         }
> > >
> > >
> > > > diff --git a/mm/mprotect.c b/mm/mprotect.c
> > > > index bc6bddd156ca..df47fc21b0e4 100644
> > > > --- a/mm/mprotect.c
> > > > +++ b/mm/mprotect.c
> > > > @@ -621,6 +621,7 @@ mprotect_fixup(struct mmu_gather *tlb, struct vm_area_struct *vma,
> > > >        * vm_flags and vm_page_prot are protected by the mmap_lock
> > > >        * held in write mode.
> > > >        */
> > > > +     vma_mark_locked(vma);
> > > >       vma->vm_flags = newflags;
> > > >       /*
> > > >        * We want to check manually if we can change individual PTEs writable
> > >
>
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