| Message ID | 20240820235730.2852400-7-Liam.Howlett@oracle.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Avoid MAP_FIXED gap exposure | expand |
On Tue, Aug 20, 2024 at 07:57:15PM GMT, Liam R. Howlett wrote: > From: "Liam R. Howlett" <Liam.Howlett@Oracle.com> > > Clean up the code by changing the munmap operation to use a structure > for the accounting and munmap variables. > > Since remove_mt() is only called in one location and the contents will > be reduced to almost nothing. The remains of the function can be added > to vms_complete_munmap_vmas(). > > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com> > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Reviewed-by: Suren Baghdasaryan <surenb@google.com> > --- > mm/vma.c | 79 ++++++++++++++++++++++++++++---------------------------- > mm/vma.h | 6 +++++ > 2 files changed, 46 insertions(+), 39 deletions(-) > > diff --git a/mm/vma.c b/mm/vma.c > index e1aee43a3dc4..7b8b8b983399 100644 > --- a/mm/vma.c > +++ b/mm/vma.c [snip] > mm = vms->mm; > @@ -731,21 +708,26 @@ static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms, > if (vms->unlock) > mmap_write_downgrade(mm); > > - prev = vma_iter_prev_range(vms->vmi); > - next = vma_next(vms->vmi); > - if (next) > - vma_iter_prev_range(vms->vmi); > - > /* > * We can free page tables without write-locking mmap_lock because VMAs > * were isolated before we downgraded mmap_lock. > */ > mas_set(mas_detach, 1); > - unmap_region(mm, mas_detach, vms->vma, prev, next, vms->start, vms->end, > - vms->vma_count, !vms->unlock); > - /* Statistics and freeing VMAs */ > + unmap_region(mm, mas_detach, vms->vma, vms->prev, vms->next, > + vms->start, vms->end, vms->vma_count, !vms->unlock); > + /* Update high watermark before we lower total_vm */ > + update_hiwater_vm(mm); > + /* Stat accounting */ > + WRITE_ONCE(mm->total_vm, READ_ONCE(mm->total_vm) - vms->nr_pages); > + mm->exec_vm -= vms->exec_vm; > + mm->stack_vm -= vms->stack_vm; > + mm->data_vm -= vms->data_vm; See below, but I bisected a bug to this patch that manifested because of miscalculated accounting. So I wonder whether it'd be a good idea to take this opportunity, when updating mm->... stats to add some: VM_WARN_ON(vms->exec_vm > mm->exec_vm); etc. for each of the fields updated. This would help catch any accounting issues like this with CONFIG_DEBUG_VM switched on. [snip] > @@ -824,6 +807,22 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, > goto munmap_gather_failed; > > vma_mark_detached(next, true); > + nrpages = vma_pages(next); > + > + vms->nr_pages += nrpages; > + if (next->vm_flags & VM_LOCKED) > + vms->locked_vm += nrpages; So I bisected a self-test failure, memfd_secret specifically, to this commit. This is because you are double-counting VM_LOCKED... > + > + if (next->vm_flags & VM_ACCOUNT) > + vms->nr_accounted += nrpages; > + > + if (is_exec_mapping(next->vm_flags)) > + vms->exec_vm += nrpages; > + else if (is_stack_mapping(next->vm_flags)) > + vms->stack_vm += nrpages; > + else if (is_data_mapping(next->vm_flags)) > + vms->data_vm += nrpages; > + > if (next->vm_flags & VM_LOCKED) > vms->locked_vm += vma_pages(next); ...the double counting being right here :) so I think we should drop the above couple lines. > > @@ -847,7 +846,9 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, > BUG_ON(next->vm_start < vms->start); > BUG_ON(next->vm_start > vms->end); > #endif > - } for_each_vma_range(*(vms->vmi), next, vms->end); > + } > + > + vms->next = vma_next(vms->vmi); > > #if defined(CONFIG_DEBUG_VM_MAPLE_TREE) > /* Make sure no VMAs are about to be lost. */ > diff --git a/mm/vma.h b/mm/vma.h > index cb67acf59012..cbf55e0e0c4f 100644 > --- a/mm/vma.h > +++ b/mm/vma.h > @@ -33,12 +33,18 @@ struct vma_munmap_struct { > struct vma_iterator *vmi; > struct mm_struct *mm; > struct vm_area_struct *vma; /* The first vma to munmap */ > + struct vm_area_struct *prev; /* vma before the munmap area */ > + struct vm_area_struct *next; /* vma after the munmap area */ > struct list_head *uf; /* Userfaultfd list_head */ > unsigned long start; /* Aligned start addr (inclusive) */ > unsigned long end; /* Aligned end addr (exclusive) */ > int vma_count; /* Number of vmas that will be removed */ > unsigned long nr_pages; /* Number of pages being removed */ > unsigned long locked_vm; /* Number of locked pages */ > + unsigned long nr_accounted; /* Number of VM_ACCOUNT pages */ > + unsigned long exec_vm; > + unsigned long stack_vm; > + unsigned long data_vm; > bool unlock; /* Unlock after the munmap */ > }; > > -- > 2.43.0 >
* Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [240821 05:59]: > On Tue, Aug 20, 2024 at 07:57:15PM GMT, Liam R. Howlett wrote: > > From: "Liam R. Howlett" <Liam.Howlett@Oracle.com> > > > > Clean up the code by changing the munmap operation to use a structure > > for the accounting and munmap variables. > > > > Since remove_mt() is only called in one location and the contents will > > be reduced to almost nothing. The remains of the function can be added > > to vms_complete_munmap_vmas(). > > > > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com> > > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > > Reviewed-by: Suren Baghdasaryan <surenb@google.com> > > --- > > mm/vma.c | 79 ++++++++++++++++++++++++++++---------------------------- > > mm/vma.h | 6 +++++ > > 2 files changed, 46 insertions(+), 39 deletions(-) > > > > diff --git a/mm/vma.c b/mm/vma.c > > index e1aee43a3dc4..7b8b8b983399 100644 > > --- a/mm/vma.c > > +++ b/mm/vma.c > > [snip] > > > mm = vms->mm; > > @@ -731,21 +708,26 @@ static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms, > > if (vms->unlock) > > mmap_write_downgrade(mm); > > > > - prev = vma_iter_prev_range(vms->vmi); > > - next = vma_next(vms->vmi); > > - if (next) > > - vma_iter_prev_range(vms->vmi); > > - > > /* > > * We can free page tables without write-locking mmap_lock because VMAs > > * were isolated before we downgraded mmap_lock. > > */ > > mas_set(mas_detach, 1); > > - unmap_region(mm, mas_detach, vms->vma, prev, next, vms->start, vms->end, > > - vms->vma_count, !vms->unlock); > > - /* Statistics and freeing VMAs */ > > + unmap_region(mm, mas_detach, vms->vma, vms->prev, vms->next, > > + vms->start, vms->end, vms->vma_count, !vms->unlock); > > + /* Update high watermark before we lower total_vm */ > > + update_hiwater_vm(mm); > > + /* Stat accounting */ > > + WRITE_ONCE(mm->total_vm, READ_ONCE(mm->total_vm) - vms->nr_pages); > > + mm->exec_vm -= vms->exec_vm; > > + mm->stack_vm -= vms->stack_vm; > > + mm->data_vm -= vms->data_vm; > > See below, but I bisected a bug to this patch that manifested because of > miscalculated accounting. So I wonder whether it'd be a good idea to take > this opportunity, when updating mm->... stats to add some: > > VM_WARN_ON(vms->exec_vm > mm->exec_vm); > > etc. for each of the fields updated. This would help catch any accounting > issues like this with CONFIG_DEBUG_VM switched on. Sounds good. > > [snip] > > > @@ -824,6 +807,22 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, > > goto munmap_gather_failed; > > > > vma_mark_detached(next, true); > > + nrpages = vma_pages(next); > > + > > + vms->nr_pages += nrpages; > > + if (next->vm_flags & VM_LOCKED) > > + vms->locked_vm += nrpages; > > So I bisected a self-test failure, memfd_secret specifically, to this > commit. This is because you are double-counting VM_LOCKED... > > > + > > + if (next->vm_flags & VM_ACCOUNT) > > + vms->nr_accounted += nrpages; > > + > > + if (is_exec_mapping(next->vm_flags)) > > + vms->exec_vm += nrpages; > > + else if (is_stack_mapping(next->vm_flags)) > > + vms->stack_vm += nrpages; > > + else if (is_data_mapping(next->vm_flags)) > > + vms->data_vm += nrpages; > > + > > if (next->vm_flags & VM_LOCKED) > > vms->locked_vm += vma_pages(next); > > ...the double counting being right here :) so I think we should drop the > above couple lines. Yeah, sure. Thanks for reviewing! > > > > > @@ -847,7 +846,9 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, > > BUG_ON(next->vm_start < vms->start); > > BUG_ON(next->vm_start > vms->end); > > #endif > > - } for_each_vma_range(*(vms->vmi), next, vms->end); > > + } > > + > > + vms->next = vma_next(vms->vmi); > > > > #if defined(CONFIG_DEBUG_VM_MAPLE_TREE) > > /* Make sure no VMAs are about to be lost. */ > > diff --git a/mm/vma.h b/mm/vma.h > > index cb67acf59012..cbf55e0e0c4f 100644 > > --- a/mm/vma.h > > +++ b/mm/vma.h > > @@ -33,12 +33,18 @@ struct vma_munmap_struct { > > struct vma_iterator *vmi; > > struct mm_struct *mm; > > struct vm_area_struct *vma; /* The first vma to munmap */ > > + struct vm_area_struct *prev; /* vma before the munmap area */ > > + struct vm_area_struct *next; /* vma after the munmap area */ > > struct list_head *uf; /* Userfaultfd list_head */ > > unsigned long start; /* Aligned start addr (inclusive) */ > > unsigned long end; /* Aligned end addr (exclusive) */ > > int vma_count; /* Number of vmas that will be removed */ > > unsigned long nr_pages; /* Number of pages being removed */ > > unsigned long locked_vm; /* Number of locked pages */ > > + unsigned long nr_accounted; /* Number of VM_ACCOUNT pages */ > > + unsigned long exec_vm; > > + unsigned long stack_vm; > > + unsigned long data_vm; > > bool unlock; /* Unlock after the munmap */ > > }; > > > > -- > > 2.43.0 > >
diff --git a/mm/vma.c b/mm/vma.c index e1aee43a3dc4..7b8b8b983399 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -103,7 +103,8 @@ static inline void init_vma_munmap(struct vma_munmap_struct *vms, vms->unlock = unlock; vms->uf = uf; vms->vma_count = 0; - vms->nr_pages = vms->locked_vm = 0; + vms->nr_pages = vms->locked_vm = vms->nr_accounted = 0; + vms->exec_vm = vms->stack_vm = vms->data_vm = 0; } /* @@ -299,30 +300,6 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, return __split_vma(vmi, vma, addr, new_below); } -/* - * Ok - we have the memory areas we should free on a maple tree so release them, - * and do the vma updates. - * - * Called with the mm semaphore held. - */ -static inline void remove_mt(struct mm_struct *mm, struct ma_state *mas) -{ - unsigned long nr_accounted = 0; - struct vm_area_struct *vma; - - /* Update high watermark before we lower total_vm */ - update_hiwater_vm(mm); - mas_for_each(mas, vma, ULONG_MAX) { - long nrpages = vma_pages(vma); - - if (vma->vm_flags & VM_ACCOUNT) - nr_accounted += nrpages; - vm_stat_account(mm, vma->vm_flags, -nrpages); - remove_vma(vma, false); - } - vm_unacct_memory(nr_accounted); -} - /* * init_vma_prep() - Initializer wrapper for vma_prepare struct * @vp: The vma_prepare struct @@ -722,7 +699,7 @@ static inline void abort_munmap_vmas(struct ma_state *mas_detach) static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms, struct ma_state *mas_detach) { - struct vm_area_struct *prev, *next; + struct vm_area_struct *vma; struct mm_struct *mm; mm = vms->mm; @@ -731,21 +708,26 @@ static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms, if (vms->unlock) mmap_write_downgrade(mm); - prev = vma_iter_prev_range(vms->vmi); - next = vma_next(vms->vmi); - if (next) - vma_iter_prev_range(vms->vmi); - /* * We can free page tables without write-locking mmap_lock because VMAs * were isolated before we downgraded mmap_lock. */ mas_set(mas_detach, 1); - unmap_region(mm, mas_detach, vms->vma, prev, next, vms->start, vms->end, - vms->vma_count, !vms->unlock); - /* Statistics and freeing VMAs */ + unmap_region(mm, mas_detach, vms->vma, vms->prev, vms->next, + vms->start, vms->end, vms->vma_count, !vms->unlock); + /* Update high watermark before we lower total_vm */ + update_hiwater_vm(mm); + /* Stat accounting */ + WRITE_ONCE(mm->total_vm, READ_ONCE(mm->total_vm) - vms->nr_pages); + mm->exec_vm -= vms->exec_vm; + mm->stack_vm -= vms->stack_vm; + mm->data_vm -= vms->data_vm; + /* Remove and clean up vmas */ mas_set(mas_detach, 0); - remove_mt(mm, mas_detach); + mas_for_each(mas_detach, vma, ULONG_MAX) + remove_vma(vma, false); + + vm_unacct_memory(vms->nr_accounted); validate_mm(mm); if (vms->unlock) mmap_read_unlock(mm); @@ -799,18 +781,19 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, if (error) goto start_split_failed; } + vms->prev = vma_prev(vms->vmi); /* * Detach a range of VMAs from the mm. Using next as a temp variable as * it is always overwritten. */ - next = vms->vma; - do { + for_each_vma_range(*(vms->vmi), next, vms->end) { + long nrpages; + if (!can_modify_vma(next)) { error = -EPERM; goto modify_vma_failed; } - /* Does it split the end? */ if (next->vm_end > vms->end) { error = __split_vma(vms->vmi, next, vms->end, 0); @@ -824,6 +807,22 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, goto munmap_gather_failed; vma_mark_detached(next, true); + nrpages = vma_pages(next); + + vms->nr_pages += nrpages; + if (next->vm_flags & VM_LOCKED) + vms->locked_vm += nrpages; + + if (next->vm_flags & VM_ACCOUNT) + vms->nr_accounted += nrpages; + + if (is_exec_mapping(next->vm_flags)) + vms->exec_vm += nrpages; + else if (is_stack_mapping(next->vm_flags)) + vms->stack_vm += nrpages; + else if (is_data_mapping(next->vm_flags)) + vms->data_vm += nrpages; + if (next->vm_flags & VM_LOCKED) vms->locked_vm += vma_pages(next); @@ -847,7 +846,9 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, BUG_ON(next->vm_start < vms->start); BUG_ON(next->vm_start > vms->end); #endif - } for_each_vma_range(*(vms->vmi), next, vms->end); + } + + vms->next = vma_next(vms->vmi); #if defined(CONFIG_DEBUG_VM_MAPLE_TREE) /* Make sure no VMAs are about to be lost. */ diff --git a/mm/vma.h b/mm/vma.h index cb67acf59012..cbf55e0e0c4f 100644 --- a/mm/vma.h +++ b/mm/vma.h @@ -33,12 +33,18 @@ struct vma_munmap_struct { struct vma_iterator *vmi; struct mm_struct *mm; struct vm_area_struct *vma; /* The first vma to munmap */ + struct vm_area_struct *prev; /* vma before the munmap area */ + struct vm_area_struct *next; /* vma after the munmap area */ struct list_head *uf; /* Userfaultfd list_head */ unsigned long start; /* Aligned start addr (inclusive) */ unsigned long end; /* Aligned end addr (exclusive) */ int vma_count; /* Number of vmas that will be removed */ unsigned long nr_pages; /* Number of pages being removed */ unsigned long locked_vm; /* Number of locked pages */ + unsigned long nr_accounted; /* Number of VM_ACCOUNT pages */ + unsigned long exec_vm; + unsigned long stack_vm; + unsigned long data_vm; bool unlock; /* Unlock after the munmap */ };