With lazy PTE page table allocation, split_huge_pmd_if_needed() and thus vma_adjust_trans_huge() can now fail if order-0 allocation for pagetable fails when trying to split. It is important to check if this failure occurred to prevent a huge PMD straddling at VMA boundary.
The vma_adjust_trans_huge() call is moved before vma_prepare() in all three callers (__split_vma, vma_shrink, commit_merge). Previously it sat between vma_prepare() and vma_complete(), where there is no mechanism to abort - once vma_prepare() has been called, we must reach vma_complete(). By moving the call earlier, a split failure can return -ENOMEM cleanly without needing to undo VMA preparation. This move is safe because vma_adjust_trans_huge() acquires its own pmd_lock() internally and does not depend on any locks or state changes from vma_prepare(). The VMA boundaries are also unchanged at the new call site, satisfying __split_huge_pmd_locked()'s requirement that the VMA covers the full PMD range. All 3 callers (__split_vma, vma_shrink, commit_merge) already return -ENOMEM if there are allocation failures for other reasons (failure in vma_iter_prealloc for example), this follows the same pattern. Signed-off-by: Usama Arif <[email protected]> --- include/linux/huge_mm.h | 13 ++++++----- mm/huge_memory.c | 21 +++++++++++++----- mm/vma.c | 37 +++++++++++++++++++++---------- tools/testing/vma/include/stubs.h | 9 ++++---- 4 files changed, 53 insertions(+), 27 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index b081ce044c735..224965fce4e66 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -483,8 +483,8 @@ int hugepage_madvise(struct vm_area_struct *vma, vm_flags_t *vm_flags, int advice); int madvise_collapse(struct vm_area_struct *vma, unsigned long start, unsigned long end, bool *lock_dropped); -void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start, - unsigned long end, struct vm_area_struct *next); +int vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start, + unsigned long end, struct vm_area_struct *next); spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma); spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma); @@ -685,11 +685,12 @@ static inline int madvise_collapse(struct vm_area_struct *vma, return -EINVAL; } -static inline void vma_adjust_trans_huge(struct vm_area_struct *vma, - unsigned long start, - unsigned long end, - struct vm_area_struct *next) +static inline int vma_adjust_trans_huge(struct vm_area_struct *vma, + unsigned long start, + unsigned long end, + struct vm_area_struct *next) { + return 0; } static inline spinlock_t *pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 976a1c74c0870..99f3b8b24c682 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3326,20 +3326,31 @@ static inline int split_huge_pmd_if_needed(struct vm_area_struct *vma, unsigned return 0; } -void vma_adjust_trans_huge(struct vm_area_struct *vma, +int vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start, unsigned long end, struct vm_area_struct *next) { + int err; + /* Check if we need to split start first. */ - split_huge_pmd_if_needed(vma, start); + err = split_huge_pmd_if_needed(vma, start); + if (err) + return err; /* Check if we need to split end next. */ - split_huge_pmd_if_needed(vma, end); + err = split_huge_pmd_if_needed(vma, end); + if (err) + return err; /* If we're incrementing next->vm_start, we might need to split it. */ - if (next) - split_huge_pmd_if_needed(next, end); + if (next) { + err = split_huge_pmd_if_needed(next, end); + if (err) + return err; + } + + return 0; } static void unmap_folio(struct folio *folio) diff --git a/mm/vma.c b/mm/vma.c index a43f3c5d4b3dd..b4a3839a8036e 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -513,6 +513,15 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, return err; } + /* + * Split any THP straddling the split boundary before splitting + * the VMA itself. Do this before vma_prepare() so we can + * cleanly fail without undoing VMA preparation. + */ + err = vma_adjust_trans_huge(vma, vma->vm_start, addr, NULL); + if (err) + return err; + new = vm_area_dup(vma); if (!new) return -ENOMEM; @@ -550,11 +559,6 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, vp.insert = new; vma_prepare(&vp); - /* - * Get rid of huge pages and shared page tables straddling the split - * boundary. - */ - vma_adjust_trans_huge(vma, vma->vm_start, addr, NULL); if (is_vm_hugetlb_page(vma)) hugetlb_split(vma, addr); @@ -732,6 +736,7 @@ static int commit_merge(struct vma_merge_struct *vmg) { struct vm_area_struct *vma; struct vma_prepare vp; + int err; if (vmg->__adjust_next_start) { /* We manipulate middle and adjust next, which is the target. */ @@ -743,6 +748,16 @@ static int commit_merge(struct vma_merge_struct *vmg) vma_iter_config(vmg->vmi, vmg->start, vmg->end); } + /* + * THP pages may need to do additional splits if we increase + * middle->vm_start. Do this before vma_prepare() so we can + * cleanly fail without undoing VMA preparation. + */ + err = vma_adjust_trans_huge(vma, vmg->start, vmg->end, + vmg->__adjust_middle_start ? vmg->middle : NULL); + if (err) + return err; + init_multi_vma_prep(&vp, vma, vmg); /* @@ -755,12 +770,6 @@ static int commit_merge(struct vma_merge_struct *vmg) return -ENOMEM; vma_prepare(&vp); - /* - * THP pages may need to do additional splits if we increase - * middle->vm_start. - */ - vma_adjust_trans_huge(vma, vmg->start, vmg->end, - vmg->__adjust_middle_start ? vmg->middle : NULL); vma_set_range(vma, vmg->start, vmg->end, vmg->pgoff); vmg_adjust_set_range(vmg); vma_iter_store_overwrite(vmg->vmi, vmg->target); @@ -1248,9 +1257,14 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma, unsigned long start, unsigned long end, pgoff_t pgoff) { struct vma_prepare vp; + int err; WARN_ON((vma->vm_start != start) && (vma->vm_end != end)); + err = vma_adjust_trans_huge(vma, start, end, NULL); + if (err) + return err; + if (vma->vm_start < start) vma_iter_config(vmi, vma->vm_start, start); else @@ -1263,7 +1277,6 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma, init_vma_prep(&vp, vma); vma_prepare(&vp); - vma_adjust_trans_huge(vma, start, end, NULL); vma_iter_clear(vmi); vma_set_range(vma, start, end, pgoff); diff --git a/tools/testing/vma/include/stubs.h b/tools/testing/vma/include/stubs.h index a30b8bc849557..952e3cc88ef10 100644 --- a/tools/testing/vma/include/stubs.h +++ b/tools/testing/vma/include/stubs.h @@ -419,11 +419,12 @@ static inline int vma_dup_policy(struct vm_area_struct *src, struct vm_area_stru return 0; } -static inline void vma_adjust_trans_huge(struct vm_area_struct *vma, - unsigned long start, - unsigned long end, - struct vm_area_struct *next) +static inline int vma_adjust_trans_huge(struct vm_area_struct *vma, + unsigned long start, + unsigned long end, + struct vm_area_struct *next) { + return 0; } static inline void hugetlb_split(struct vm_area_struct *, unsigned long) {} -- 2.52.0
