| Message ID | 155836081252.2441.9024100415314519956.stgit@localhost.localdomain (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: process_vm_mmap() -- syscall for duplication a process mapping | expand |
On Mon, May 20, 2019 at 05:00:12PM +0300, Kirill Tkhai wrote: > This prepares the function to copy a vma between > two processes. Two new arguments are introduced. This kind of changes requires a lot more explanation in commit message, describing all possible corner cases. For instance, I would really like to see a story on why logic around need_rmap_locks is safe after the change. > > Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> > --- > include/linux/mm.h | 4 ++-- > mm/mmap.c | 33 ++++++++++++++++++++++++--------- > mm/mremap.c | 4 ++-- > 3 files changed, 28 insertions(+), 13 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 0e8834ac32b7..afe07e4a76f8 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2329,8 +2329,8 @@ extern void __vma_link_rb(struct mm_struct *, struct vm_area_struct *, > struct rb_node **, struct rb_node *); > extern void unlink_file_vma(struct vm_area_struct *); > extern struct vm_area_struct *copy_vma(struct vm_area_struct **, > - unsigned long addr, unsigned long len, pgoff_t pgoff, > - bool *need_rmap_locks); > + struct mm_struct *, unsigned long addr, unsigned long len, > + pgoff_t pgoff, bool *need_rmap_locks, bool clear_flags_ctx); > extern void exit_mmap(struct mm_struct *); > > static inline int check_data_rlimit(unsigned long rlim, > diff --git a/mm/mmap.c b/mm/mmap.c > index 57803a0a3a5c..99778e724ad1 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -3195,19 +3195,21 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma) > } > > /* > - * Copy the vma structure to a new location in the same mm, > - * prior to moving page table entries, to effect an mremap move. > + * Copy the vma structure to new location in the same vma > + * prior to moving page table entries, to effect an mremap move; > */ > struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, > - unsigned long addr, unsigned long len, pgoff_t pgoff, > - bool *need_rmap_locks) > + struct mm_struct *mm, unsigned long addr, > + unsigned long len, pgoff_t pgoff, > + bool *need_rmap_locks, bool clear_flags_ctx) > { > struct vm_area_struct *vma = *vmap; > unsigned long vma_start = vma->vm_start; > - struct mm_struct *mm = vma->vm_mm; > + struct vm_userfaultfd_ctx uctx; > struct vm_area_struct *new_vma, *prev; > struct rb_node **rb_link, *rb_parent; > bool faulted_in_anon_vma = true; > + unsigned long flags; > > /* > * If anonymous vma has not yet been faulted, update new pgoff > @@ -3220,15 +3222,25 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, > > if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) > return NULL; /* should never get here */ > - new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags, > - vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma), > - vma->vm_userfaultfd_ctx); > + > + uctx = vma->vm_userfaultfd_ctx; > + flags = vma->vm_flags; > + if (clear_flags_ctx) { > + uctx = NULL_VM_UFFD_CTX; > + flags &= ~(VM_UFFD_MISSING | VM_UFFD_WP | VM_MERGEABLE | > + VM_LOCKED | VM_LOCKONFAULT | VM_WIPEONFORK | > + VM_DONTCOPY); > + } Why is the new logic required? No justification given. > + > + new_vma = vma_merge(mm, prev, addr, addr + len, flags, vma->anon_vma, > + vma->vm_file, pgoff, vma_policy(vma), uctx); > if (new_vma) { > /* > * Source vma may have been merged into new_vma > */ > if (unlikely(vma_start >= new_vma->vm_start && > - vma_start < new_vma->vm_end)) { > + vma_start < new_vma->vm_end) && > + vma->vm_mm == mm) { How can vma_merge() succeed if vma->vm_mm != mm? > /* > * The only way we can get a vma_merge with > * self during an mremap is if the vma hasn't > @@ -3249,6 +3261,9 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, > new_vma = vm_area_dup(vma); > if (!new_vma) > goto out; > + new_vma->vm_mm = mm; > + new_vma->vm_flags = flags; > + new_vma->vm_userfaultfd_ctx = uctx; > new_vma->vm_start = addr; > new_vma->vm_end = addr + len; > new_vma->vm_pgoff = pgoff; > diff --git a/mm/mremap.c b/mm/mremap.c > index 37b5b2ad91be..9a96cfc28675 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -352,8 +352,8 @@ static unsigned long move_vma(struct vm_area_struct *vma, > return err; > > new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT); > - new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff, > - &need_rmap_locks); > + new_vma = copy_vma(&vma, mm, new_addr, new_len, new_pgoff, > + &need_rmap_locks, false); > if (!new_vma) > return -ENOMEM; > >
Hi, Kirill, On 21.05.2019 11:18, Kirill A. Shutemov wrote: > On Mon, May 20, 2019 at 05:00:12PM +0300, Kirill Tkhai wrote: >> This prepares the function to copy a vma between >> two processes. Two new arguments are introduced. > > This kind of changes requires a lot more explanation in commit message, > describing all possible corner cases> For instance, I would really like to see a story on why logic around > need_rmap_locks is safe after the change. Let me fast answer on the below question firstly, and later I'll write wide explanations, since this requires much more time. >> >> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> >> --- >> include/linux/mm.h | 4 ++-- >> mm/mmap.c | 33 ++++++++++++++++++++++++--------- >> mm/mremap.c | 4 ++-- >> 3 files changed, 28 insertions(+), 13 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 0e8834ac32b7..afe07e4a76f8 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -2329,8 +2329,8 @@ extern void __vma_link_rb(struct mm_struct *, struct vm_area_struct *, >> struct rb_node **, struct rb_node *); >> extern void unlink_file_vma(struct vm_area_struct *); >> extern struct vm_area_struct *copy_vma(struct vm_area_struct **, >> - unsigned long addr, unsigned long len, pgoff_t pgoff, >> - bool *need_rmap_locks); >> + struct mm_struct *, unsigned long addr, unsigned long len, >> + pgoff_t pgoff, bool *need_rmap_locks, bool clear_flags_ctx); >> extern void exit_mmap(struct mm_struct *); >> >> static inline int check_data_rlimit(unsigned long rlim, >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 57803a0a3a5c..99778e724ad1 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -3195,19 +3195,21 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma) >> } >> >> /* >> - * Copy the vma structure to a new location in the same mm, >> - * prior to moving page table entries, to effect an mremap move. >> + * Copy the vma structure to new location in the same vma >> + * prior to moving page table entries, to effect an mremap move; >> */ >> struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, >> - unsigned long addr, unsigned long len, pgoff_t pgoff, >> - bool *need_rmap_locks) >> + struct mm_struct *mm, unsigned long addr, >> + unsigned long len, pgoff_t pgoff, >> + bool *need_rmap_locks, bool clear_flags_ctx) >> { >> struct vm_area_struct *vma = *vmap; >> unsigned long vma_start = vma->vm_start; >> - struct mm_struct *mm = vma->vm_mm; >> + struct vm_userfaultfd_ctx uctx; >> struct vm_area_struct *new_vma, *prev; >> struct rb_node **rb_link, *rb_parent; >> bool faulted_in_anon_vma = true; >> + unsigned long flags; >> >> /* >> * If anonymous vma has not yet been faulted, update new pgoff >> @@ -3220,15 +3222,25 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, >> >> if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) >> return NULL; /* should never get here */ >> - new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags, >> - vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma), >> - vma->vm_userfaultfd_ctx); >> + >> + uctx = vma->vm_userfaultfd_ctx; >> + flags = vma->vm_flags; >> + if (clear_flags_ctx) { >> + uctx = NULL_VM_UFFD_CTX; >> + flags &= ~(VM_UFFD_MISSING | VM_UFFD_WP | VM_MERGEABLE | >> + VM_LOCKED | VM_LOCKONFAULT | VM_WIPEONFORK | >> + VM_DONTCOPY); >> + } > > Why is the new logic required? No justification given. Ditto. >> + >> + new_vma = vma_merge(mm, prev, addr, addr + len, flags, vma->anon_vma, >> + vma->vm_file, pgoff, vma_policy(vma), uctx); >> if (new_vma) { >> /* >> * Source vma may have been merged into new_vma >> */ >> if (unlikely(vma_start >= new_vma->vm_start && >> - vma_start < new_vma->vm_end)) { >> + vma_start < new_vma->vm_end) && >> + vma->vm_mm == mm) { > > How can vma_merge() succeed if vma->vm_mm != mm? We don't use vma as an argument of vma_merge(). We use vma as a source of vma->anon_vma, vma->vm_file and vma_policy(). We search some new_vma in mm with the same characteristics as vma has in vma->vm_mm. In case of success vma_merge() returns it for us. For example, it may success, when vma->vm_mm is mm_struct of forked process, while mm is mm_struct of its parent. [...] Kirill
diff --git a/include/linux/mm.h b/include/linux/mm.h index 0e8834ac32b7..afe07e4a76f8 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2329,8 +2329,8 @@ extern void __vma_link_rb(struct mm_struct *, struct vm_area_struct *, struct rb_node **, struct rb_node *); extern void unlink_file_vma(struct vm_area_struct *); extern struct vm_area_struct *copy_vma(struct vm_area_struct **, - unsigned long addr, unsigned long len, pgoff_t pgoff, - bool *need_rmap_locks); + struct mm_struct *, unsigned long addr, unsigned long len, + pgoff_t pgoff, bool *need_rmap_locks, bool clear_flags_ctx); extern void exit_mmap(struct mm_struct *); static inline int check_data_rlimit(unsigned long rlim, diff --git a/mm/mmap.c b/mm/mmap.c index 57803a0a3a5c..99778e724ad1 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3195,19 +3195,21 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma) } /* - * Copy the vma structure to a new location in the same mm, - * prior to moving page table entries, to effect an mremap move. + * Copy the vma structure to new location in the same vma + * prior to moving page table entries, to effect an mremap move; */ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, - unsigned long addr, unsigned long len, pgoff_t pgoff, - bool *need_rmap_locks) + struct mm_struct *mm, unsigned long addr, + unsigned long len, pgoff_t pgoff, + bool *need_rmap_locks, bool clear_flags_ctx) { struct vm_area_struct *vma = *vmap; unsigned long vma_start = vma->vm_start; - struct mm_struct *mm = vma->vm_mm; + struct vm_userfaultfd_ctx uctx; struct vm_area_struct *new_vma, *prev; struct rb_node **rb_link, *rb_parent; bool faulted_in_anon_vma = true; + unsigned long flags; /* * If anonymous vma has not yet been faulted, update new pgoff @@ -3220,15 +3222,25 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) return NULL; /* should never get here */ - new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags, - vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma), - vma->vm_userfaultfd_ctx); + + uctx = vma->vm_userfaultfd_ctx; + flags = vma->vm_flags; + if (clear_flags_ctx) { + uctx = NULL_VM_UFFD_CTX; + flags &= ~(VM_UFFD_MISSING | VM_UFFD_WP | VM_MERGEABLE | + VM_LOCKED | VM_LOCKONFAULT | VM_WIPEONFORK | + VM_DONTCOPY); + } + + new_vma = vma_merge(mm, prev, addr, addr + len, flags, vma->anon_vma, + vma->vm_file, pgoff, vma_policy(vma), uctx); if (new_vma) { /* * Source vma may have been merged into new_vma */ if (unlikely(vma_start >= new_vma->vm_start && - vma_start < new_vma->vm_end)) { + vma_start < new_vma->vm_end) && + vma->vm_mm == mm) { /* * The only way we can get a vma_merge with * self during an mremap is if the vma hasn't @@ -3249,6 +3261,9 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, new_vma = vm_area_dup(vma); if (!new_vma) goto out; + new_vma->vm_mm = mm; + new_vma->vm_flags = flags; + new_vma->vm_userfaultfd_ctx = uctx; new_vma->vm_start = addr; new_vma->vm_end = addr + len; new_vma->vm_pgoff = pgoff; diff --git a/mm/mremap.c b/mm/mremap.c index 37b5b2ad91be..9a96cfc28675 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -352,8 +352,8 @@ static unsigned long move_vma(struct vm_area_struct *vma, return err; new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT); - new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff, - &need_rmap_locks); + new_vma = copy_vma(&vma, mm, new_addr, new_len, new_pgoff, + &need_rmap_locks, false); if (!new_vma) return -ENOMEM;
This prepares the function to copy a vma between two processes. Two new arguments are introduced. Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> --- include/linux/mm.h | 4 ++-- mm/mmap.c | 33 ++++++++++++++++++++++++--------- mm/mremap.c | 4 ++-- 3 files changed, 28 insertions(+), 13 deletions(-)