Messages in this thread | | | Date | Wed, 3 May 2023 16:31:36 +0200 | From | David Hildenbrand <> | Subject | Re: [PATCH v8 1/3] mm/mmap: separate writenotify and dirty tracking logic |
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On 03.05.23 00:51, Lorenzo Stoakes wrote: > vma_wants_writenotify() is specifically intended for setting PTE page table > flags, accounting for existing page table flag state and whether the > filesystem performs dirty tracking. > > Separate out the notions of dirty tracking and PTE write notify checking in > order that we can invoke the dirty tracking check from elsewhere. > > Note that this change introduces a very small duplicate check of the > separated out vm_ops_needs_writenotify() and vma_is_shared_writable() > functions. This is necessary to avoid making vma_needs_dirty_tracking() > needlessly complicated (e.g. passing flags or having it assume checks were > already performed). This is small enough that it doesn't seem too > egregious. > > We check to ensure the mapping is shared writable, as any GUP caller will > be safe - MAP_PRIVATE mappings will be CoW'd and read-only file-backed > shared mappings are not permitted access, even with FOLL_FORCE. > > Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> > Reviewed-by: John Hubbard <jhubbard@nvidia.com> > Reviewed-by: Mika Penttilä <mpenttil@redhat.com> > Reviewed-by: Jan Kara <jack@suse.cz> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> > --- > include/linux/mm.h | 1 + > mm/mmap.c | 53 ++++++++++++++++++++++++++++++++++------------ > 2 files changed, 41 insertions(+), 13 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 27ce77080c79..7b1d4e7393ef 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2422,6 +2422,7 @@ extern unsigned long move_page_tables(struct vm_area_struct *vma, > #define MM_CP_UFFD_WP_ALL (MM_CP_UFFD_WP | \ > MM_CP_UFFD_WP_RESOLVE) > > +bool vma_needs_dirty_tracking(struct vm_area_struct *vma); > int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot); > static inline bool vma_wants_manual_pte_write_upgrade(struct vm_area_struct *vma) > { > diff --git a/mm/mmap.c b/mm/mmap.c > index 5522130ae606..fa7442e44cc2 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1475,6 +1475,42 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg) > } > #endif /* __ARCH_WANT_SYS_OLD_MMAP */ > > +/* Do VMA operations imply write notify is required? */
Nit: comment is superfluous, this is already self-documenting code.
> +static bool vm_ops_needs_writenotify(const struct vm_operations_struct *vm_ops) > +{ > + return vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite); > +} > + > +/* Is this VMA shared and writable? */
Nit: dito
> +static bool vma_is_shared_writable(struct vm_area_struct *vma) > +{ > + return (vma->vm_flags & (VM_WRITE | VM_SHARED)) == > + (VM_WRITE | VM_SHARED); > +} > + > +/* > + * Does this VMA require the underlying folios to have their dirty state > + * tracked? > + */
Nit: dito
> +bool vma_needs_dirty_tracking(struct vm_area_struct *vma) > +{ > + /* Only shared, writable VMAs require dirty tracking. */ > + if (!vma_is_shared_writable(vma)) > + return false; > + > + /* Does the filesystem need to be notified? */ > + if (vm_ops_needs_writenotify(vma->vm_ops)) > + return true; > + > + /* Specialty mapping? */ > + if (vma->vm_flags & VM_PFNMAP) > + return false; > + > + /* Can the mapping track the dirty pages? */ > + return vma->vm_file && vma->vm_file->f_mapping && > + mapping_can_writeback(vma->vm_file->f_mapping); > +} > + > /* > * Some shared mappings will want the pages marked read-only > * to track write events. If so, we'll downgrade vm_page_prot > @@ -1483,21 +1519,18 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg) > */ > int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot) > { > - vm_flags_t vm_flags = vma->vm_flags; > - const struct vm_operations_struct *vm_ops = vma->vm_ops; > - > /* If it was private or non-writable, the write bit is already clear */ > - if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED))) > + if (!vma_is_shared_writable(vma)) > return 0; > > /* The backer wishes to know when pages are first written to? */ > - if (vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite)) > + if (vm_ops_needs_writenotify(vma->vm_ops)) > return 1; > > /* The open routine did something to the protections that pgprot_modify > * won't preserve? */ > if (pgprot_val(vm_page_prot) != > - pgprot_val(vm_pgprot_modify(vm_page_prot, vm_flags))) > + pgprot_val(vm_pgprot_modify(vm_page_prot, vma->vm_flags))) > return 0; > > /* > @@ -1511,13 +1544,7 @@ int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot) > if (userfaultfd_wp(vma)) > return 1; > > - /* Specialty mapping? */ > - if (vm_flags & VM_PFNMAP) > - return 0; > - > - /* Can the mapping track the dirty pages? */ > - return vma->vm_file && vma->vm_file->f_mapping && > - mapping_can_writeback(vma->vm_file->f_mapping); > + return vma_needs_dirty_tracking(vma); > } > > /*
We now have duplicate vma_is_shared_writable() and vm_ops_needs_writenotify() checks ...
Maybe move the VM_PFNMAP and "/* Can the mapping track the dirty pages? */" checks into a separate helper and call that from both, vma_wants_writenotify() and vma_needs_dirty_tracking() ?
In any case
Acked-by: David Hildenbrand <david@redhat.com>
-- Thanks,
David / dhildenb
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