On Wed 25-01-23 00:38:50, Suren Baghdasaryan wrote:
> In cases when VMA flags are modified after VMA was isolated and mmap_lock
> was downgraded, flags modifications would result in an assertion because
> mmap write lock is not held.
> Introduce mod_vm_flags_nolock to be used in such situation.
> Pass a hint to untrack_pfn to conditionally use mod_vm_flags_nolock for
> flags modification and to avoid assertion.
The changelog nor the documentation of mod_vm_flags_nolock
really explain when it is safe to use it. This is really important for
future potential users.
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---
> arch/x86/mm/pat/memtype.c | 10 +++++++---
> include/linux/mm.h | 12 +++++++++---
> include/linux/pgtable.h | 5 +++--
> mm/memory.c | 13 +++++++------
> mm/memremap.c | 4 ++--
> mm/mmap.c | 16 ++++++++++------
> 6 files changed, 38 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
> index ae9645c900fa..d8adc0b42cf2 100644
> --- a/arch/x86/mm/pat/memtype.c
> +++ b/arch/x86/mm/pat/memtype.c
> @@ -1046,7 +1046,7 @@ void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot, pfn_t pfn)
> * can be for the entire vma (in which case pfn, size are zero).
> */
> void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
> - unsigned long size)
> + unsigned long size, bool mm_wr_locked)
> {
> resource_size_t paddr;
> unsigned long prot;
> @@ -1065,8 +1065,12 @@ void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
> size = vma->vm_end - vma->vm_start;
> }
> free_pfn_range(paddr, size);
> - if (vma)
> - clear_vm_flags(vma, VM_PAT);
> + if (vma) {
> + if (mm_wr_locked)
> + clear_vm_flags(vma, VM_PAT);
> + else
> + mod_vm_flags_nolock(vma, 0, VM_PAT);
> + }
> }
>
> /*
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 55335edd1373..48d49930c411 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -656,12 +656,18 @@ static inline void clear_vm_flags(struct vm_area_struct *vma,
> vma->vm_flags &= ~flags;
> }
>
> +static inline void mod_vm_flags_nolock(struct vm_area_struct *vma,
> + unsigned long set, unsigned long clear)
> +{
> + vma->vm_flags |= set;
> + vma->vm_flags &= ~clear;
> +}
> +
> static inline void mod_vm_flags(struct vm_area_struct *vma,
> unsigned long set, unsigned long clear)
> {
> mmap_assert_write_locked(vma->vm_mm);
> - vma->vm_flags |= set;
> - vma->vm_flags &= ~clear;
> + mod_vm_flags_nolock(vma, set, clear);
> }
>
> static inline void vma_set_anonymous(struct vm_area_struct *vma)
> @@ -2087,7 +2093,7 @@ static inline void zap_vma_pages(struct vm_area_struct *vma)
> }
> void unmap_vmas(struct mmu_gather *tlb, struct maple_tree *mt,
> struct vm_area_struct *start_vma, unsigned long start,
> - unsigned long end);
> + unsigned long end, bool mm_wr_locked);
>
> struct mmu_notifier_range;
>
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 5fd45454c073..c63cd44777ec 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1185,7 +1185,8 @@ static inline int track_pfn_copy(struct vm_area_struct *vma)
> * can be for the entire vma (in which case pfn, size are zero).
> */
> static inline void untrack_pfn(struct vm_area_struct *vma,
> - unsigned long pfn, unsigned long size)
> + unsigned long pfn, unsigned long size,
> + bool mm_wr_locked)
> {
> }
>
> @@ -1203,7 +1204,7 @@ extern void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot,
> pfn_t pfn);
> extern int track_pfn_copy(struct vm_area_struct *vma);
> extern void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
> - unsigned long size);
> + unsigned long size, bool mm_wr_locked);
> extern void untrack_pfn_moved(struct vm_area_struct *vma);
> #endif
>
> diff --git a/mm/memory.c b/mm/memory.c
> index d6902065e558..5b11b50e2c4a 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1613,7 +1613,7 @@ void unmap_page_range(struct mmu_gather *tlb,
> static void unmap_single_vma(struct mmu_gather *tlb,
> struct vm_area_struct *vma, unsigned long start_addr,
> unsigned long end_addr,
> - struct zap_details *details)
> + struct zap_details *details, bool mm_wr_locked)
> {
> unsigned long start = max(vma->vm_start, start_addr);
> unsigned long end;
> @@ -1628,7 +1628,7 @@ static void unmap_single_vma(struct mmu_gather *tlb,
> uprobe_munmap(vma, start, end);
>
> if (unlikely(vma->vm_flags & VM_PFNMAP))
> - untrack_pfn(vma, 0, 0);
> + untrack_pfn(vma, 0, 0, mm_wr_locked);
>
> if (start != end) {
> if (unlikely(is_vm_hugetlb_page(vma))) {
> @@ -1675,7 +1675,7 @@ static void unmap_single_vma(struct mmu_gather *tlb,
> */
> void unmap_vmas(struct mmu_gather *tlb, struct maple_tree *mt,
> struct vm_area_struct *vma, unsigned long start_addr,
> - unsigned long end_addr)
> + unsigned long end_addr, bool mm_wr_locked)
> {
> struct mmu_notifier_range range;
> struct zap_details details = {
> @@ -1689,7 +1689,8 @@ void unmap_vmas(struct mmu_gather *tlb, struct maple_tree *mt,
> start_addr, end_addr);
> mmu_notifier_invalidate_range_start(&range);
> do {
> - unmap_single_vma(tlb, vma, start_addr, end_addr, &details);
> + unmap_single_vma(tlb, vma, start_addr, end_addr, &details,
> + mm_wr_locked);
> } while ((vma = mas_find(&mas, end_addr - 1)) != NULL);
> mmu_notifier_invalidate_range_end(&range);
> }
> @@ -1723,7 +1724,7 @@ void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
> * unmap 'address-end' not 'range.start-range.end' as range
> * could have been expanded for hugetlb pmd sharing.
> */
> - unmap_single_vma(&tlb, vma, address, end, details);
> + unmap_single_vma(&tlb, vma, address, end, details, false);
> mmu_notifier_invalidate_range_end(&range);
> tlb_finish_mmu(&tlb);
> }
> @@ -2492,7 +2493,7 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
>
> err = remap_pfn_range_notrack(vma, addr, pfn, size, prot);
> if (err)
> - untrack_pfn(vma, pfn, PAGE_ALIGN(size));
> + untrack_pfn(vma, pfn, PAGE_ALIGN(size), true);
> return err;
> }
> EXPORT_SYMBOL(remap_pfn_range);
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 08cbf54fe037..2f88f43d4a01 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -129,7 +129,7 @@ static void pageunmap_range(struct dev_pagemap *pgmap, int range_id)
> }
> mem_hotplug_done();
>
> - untrack_pfn(NULL, PHYS_PFN(range->start), range_len(range));
> + untrack_pfn(NULL, PHYS_PFN(range->start), range_len(range), true);
> pgmap_array_delete(range);
> }
>
> @@ -276,7 +276,7 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
> if (!is_private)
> kasan_remove_zero_shadow(__va(range->start), range_len(range));
> err_kasan:
> - untrack_pfn(NULL, PHYS_PFN(range->start), range_len(range));
> + untrack_pfn(NULL, PHYS_PFN(range->start), range_len(range), true);
> err_pfn_remap:
> pgmap_array_delete(range);
> return error;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 2c6e9072e6a8..69d440997648 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -78,7 +78,7 @@ core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644);
> static void unmap_region(struct mm_struct *mm, struct maple_tree *mt,
> struct vm_area_struct *vma, struct vm_area_struct *prev,
> struct vm_area_struct *next, unsigned long start,
> - unsigned long end);
> + unsigned long end, bool mm_wr_locked);
>
> static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
> {
> @@ -2136,14 +2136,14 @@ static inline void remove_mt(struct mm_struct *mm, struct ma_state *mas)
> static void unmap_region(struct mm_struct *mm, struct maple_tree *mt,
> struct vm_area_struct *vma, struct vm_area_struct *prev,
> struct vm_area_struct *next,
> - unsigned long start, unsigned long end)
> + unsigned long start, unsigned long end, bool mm_wr_locked)
> {
> struct mmu_gather tlb;
>
> lru_add_drain();
> tlb_gather_mmu(&tlb, mm);
> update_hiwater_rss(mm);
> - unmap_vmas(&tlb, mt, vma, start, end);
> + unmap_vmas(&tlb, mt, vma, start, end, mm_wr_locked);
> free_pgtables(&tlb, mt, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
> next ? next->vm_start : USER_PGTABLES_CEILING);
> tlb_finish_mmu(&tlb);
> @@ -2391,7 +2391,11 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
> mmap_write_downgrade(mm);
> }
>
> - unmap_region(mm, &mt_detach, vma, prev, next, start, end);
> + /*
> + * We can free page tables without write-locking mmap_lock because VMAs
> + * were isolated before we downgraded mmap_lock.
> + */
> + unmap_region(mm, &mt_detach, vma, prev, next, start, end, !downgrade);
> /* Statistics and freeing VMAs */
> mas_set(&mas_detach, start);
> remove_mt(mm, &mas_detach);
> @@ -2704,7 +2708,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>
> /* Undo any partial mapping done by a device driver. */
> unmap_region(mm, &mm->mm_mt, vma, prev, next, vma->vm_start,
> - vma->vm_end);
> + vma->vm_end, true);
> }
> if (file && (vm_flags & VM_SHARED))
> mapping_unmap_writable(file->f_mapping);
> @@ -3031,7 +3035,7 @@ void exit_mmap(struct mm_struct *mm)
> tlb_gather_mmu_fullmm(&tlb, mm);
> /* update_hiwater_rss(mm) here? but nobody should be looking */
> /* Use ULONG_MAX here to ensure all VMAs in the mm are unmapped */
> - unmap_vmas(&tlb, &mm->mm_mt, vma, 0, ULONG_MAX);
> + unmap_vmas(&tlb, &mm->mm_mt, vma, 0, ULONG_MAX, false);
> mmap_read_unlock(mm);
>
> /*
> --
> 2.39.1
--
Michal Hocko
SUSE Labs
