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List-Subscribe: List-Unsubscribe: On Wed, Sep 03, 2025 at 04:19:04PM -0400, Liam R. Howlett wrote: > * Lorenzo Stoakes [250819 15:14]: > > On Fri, Aug 15, 2025 at 03:10:29PM -0400, Liam R. Howlett wrote: > > > The ceiling and tree search limit need to be different arguments for the > > > future change in the failed fork attempt. > > > > > > No functional changes intended. > > > > > > Signed-off-by: Liam R. Howlett > > > > (Obv. in addition to comment about broken VMA tests :P) > > > > I guess intent is that if we discover any page tables beyond tree_max then > > we ought to just wipe them all out so, in effect, we don't consider > > mappings at or past tree_max to be valid? > > Actually... there are some archs that map outside the vma and they are > valid.. I think mips? and I think lower, but yeah.. it's needed. This > is why prev->vm_end and next->vm_start are used as page table limits, > afaik. This is a serious annoyance because it frequently adds walks > that are infrequently necessary to the vma tree. ugh god. I was vaguely aware of this but that's gross. Very gross. I need to document all the VMA weirdnesses smoewhere. What do they do this for? Guard pages or something? > > > > > I feel like we need a comment to this effect as this is confusing as it is. > > > > Could we add a kerneldoc comment for free_pgtables() spelling this out? > > I'll add a note here, but confusion will probably increase. I'll add a > note about the tree max as well. Thanks! > > > > > > --- > > > mm/internal.h | 4 +++- > > > mm/memory.c | 7 ++++--- > > > mm/mmap.c | 2 +- > > > mm/vma.c | 3 ++- > > > 4 files changed, 10 insertions(+), 6 deletions(-) > > > > > > diff --git a/mm/internal.h b/mm/internal.h > > > index 45b725c3dc030..f9a278ac76d83 100644 > > > --- a/mm/internal.h > > > +++ b/mm/internal.h > > > @@ -444,7 +444,9 @@ void folio_activate(struct folio *folio); > > > > > > void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas, > > > struct vm_area_struct *start_vma, unsigned long floor, > > > - unsigned long ceiling, bool mm_wr_locked); > > > + unsigned long ceiling, unsigned long tree_max, > > > + bool mm_wr_locked); > > > + > > > void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte); > > > > > > struct zap_details; > > > diff --git a/mm/memory.c b/mm/memory.c > > > index 0ba4f6b718471..3346514562bba 100644 > > > --- a/mm/memory.c > > > +++ b/mm/memory.c > > > @@ -371,7 +371,8 @@ void free_pgd_range(struct mmu_gather *tlb, > > > > > > void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas, > > > struct vm_area_struct *vma, unsigned long floor, > > > - unsigned long ceiling, bool mm_wr_locked) > > > + unsigned long ceiling, unsigned long tree_max, > > > + bool mm_wr_locked) > > > { > > > struct unlink_vma_file_batch vb; > > > > > > @@ -385,7 +386,7 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas, > > > * Note: USER_PGTABLES_CEILING may be passed as ceiling and may > > > * be 0. This will underflow and is okay. > > > */ > > > - next = mas_find(mas, ceiling - 1); > > > + next = mas_find(mas, tree_max - 1); > > > > Do we need to put some sort of sanity checks in to make sure tree_max <= ceiling > > (though this 0 case is a pain... so I guess tree_max - 1 <= ceiling - 1?) > > Sure! Thanks!