Re: [PATCH v2 17/26] userfaultfd: wp: support swap and page migration

Mike Rapoport
2019-02-25T18:29:06Z

On Tue, Feb 12, 2019 at 10:56:23AM +0800, Peter Xu wrote:
> For either swap and page migration, we all use the bit 2 of the entry to
> identify whether this entry is uffd write-protected. It plays a similar
> role as the existing soft dirty bit in swap entries but only for keeping
> the uffd-wp tracking for a specific PTE/PMD.
>
> Something special here is that when we want to recover the uffd-wp bit
> from a swap/migration entry to the PTE bit we'll also need to take care
> of the _PAGE_RW bit and make sure it's cleared, otherwise even with the
> _PAGE_UFFD_WP bit we can't trap it at all.
>
> Note that this patch removed two lines from "userfaultfd: wp: hook
> userfault handler to write protection fault" where we try to remove the
> VM_FAULT_WRITE from vmf->flags when uffd-wp is set for the VMA. This
> patch will still keep the write flag there.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>

> ---
> include/linux/swapops.h | 2 ++
> mm/huge_memory.c | 3 +++
> mm/memory.c | 8 ++++++--
> mm/migrate.c | 7 +++++++
> mm/mprotect.c | 2 ++
> mm/rmap.c | 6 ++++++
> 6 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index 4d961668e5fc..0c2923b1cdb7 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -68,6 +68,8 @@ static inline swp_entry_t pte_to_swp_entry(pte_t pte)
>
> if (pte_swp_soft_dirty(pte))
> pte = pte_swp_clear_soft_dirty(pte);
> + if (pte_swp_uffd_wp(pte))
> + pte = pte_swp_clear_uffd_wp(pte);
> arch_entry = __pte_to_swp_entry(pte);
> return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
> }
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index fb2234cb595a..75de07141801 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2175,6 +2175,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> write = is_write_migration_entry(entry);
> young = false;
> soft_dirty = pmd_swp_soft_dirty(old_pmd);
> + uffd_wp = pmd_swp_uffd_wp(old_pmd);
> } else {
> page = pmd_page(old_pmd);
> if (pmd_dirty(old_pmd))
> @@ -2207,6 +2208,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> entry = swp_entry_to_pte(swp_entry);
> if (soft_dirty)
> entry = pte_swp_mksoft_dirty(entry);
> + if (uffd_wp)
> + entry = pte_swp_mkuffd_wp(entry);
> } else {
> entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
> entry = maybe_mkwrite(entry, vma);
> diff --git a/mm/memory.c b/mm/memory.c
> index c2035539e9fd..7cee990d67cf 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -736,6 +736,8 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> pte = swp_entry_to_pte(entry);
> if (pte_swp_soft_dirty(*src_pte))
> pte = pte_swp_mksoft_dirty(pte);
> + if (pte_swp_uffd_wp(*src_pte))
> + pte = pte_swp_mkuffd_wp(pte);
> set_pte_at(src_mm, addr, src_pte, pte);
> }
> } else if (is_device_private_entry(entry)) {
> @@ -2815,8 +2817,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
> dec_mm_counter_fast(vma->vm_mm, MM_SWAPENTS);
> pte = mk_pte(page, vma->vm_page_prot);
> - if (userfaultfd_wp(vma))
> - vmf->flags &= ~FAULT_FLAG_WRITE;
> if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) {
> pte = maybe_mkwrite(pte_mkdirty(pte), vma);
> vmf->flags &= ~FAULT_FLAG_WRITE;
> @@ -2826,6 +2826,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> flush_icache_page(vma, page);
> if (pte_swp_soft_dirty(vmf->orig_pte))
> pte = pte_mksoft_dirty(pte);
> + if (pte_swp_uffd_wp(vmf->orig_pte)) {
> + pte = pte_mkuffd_wp(pte);
> + pte = pte_wrprotect(pte);
> + }
> set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
> arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
> vmf->orig_pte = pte;
> diff --git a/mm/migrate.c b/mm/migrate.c
> index d4fd680be3b0..605ccd1f5c64 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -242,6 +242,11 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
> if (is_write_migration_entry(entry))
> pte = maybe_mkwrite(pte, vma);
>
> + if (pte_swp_uffd_wp(*pvmw.pte)) {
> + pte = pte_mkuffd_wp(pte);
> + pte = pte_wrprotect(pte);
> + }
> +
> if (unlikely(is_zone_device_page(new))) {
> if (is_device_private_page(new)) {
> entry = make_device_private_entry(new, pte_write(pte));
> @@ -2290,6 +2295,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> swp_pte = swp_entry_to_pte(entry);
> if (pte_soft_dirty(pte))
> swp_pte = pte_swp_mksoft_dirty(swp_pte);
> + if (pte_uffd_wp(pte))
> + swp_pte = pte_swp_mkuffd_wp(swp_pte);
> set_pte_at(mm, addr, ptep, swp_pte);
>
> /*
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index ae93721f3795..73a65f07fe41 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -187,6 +187,8 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> newpte = swp_entry_to_pte(entry);
> if (pte_swp_soft_dirty(oldpte))
> newpte = pte_swp_mksoft_dirty(newpte);
> + if (pte_swp_uffd_wp(oldpte))
> + newpte = pte_swp_mkuffd_wp(newpte);
> set_pte_at(mm, addr, pte, newpte);
>
> pages++;
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 0454ecc29537..3750d5a5283c 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1469,6 +1469,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> swp_pte = swp_entry_to_pte(entry);
> if (pte_soft_dirty(pteval))
> swp_pte = pte_swp_mksoft_dirty(swp_pte);
> + if (pte_uffd_wp(pteval))
> + swp_pte = pte_swp_mkuffd_wp(swp_pte);
> set_pte_at(mm, pvmw.address, pvmw.pte, swp_pte);
> /*
> * No need to invalidate here it will synchronize on
> @@ -1561,6 +1563,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> swp_pte = swp_entry_to_pte(entry);
> if (pte_soft_dirty(pteval))
> swp_pte = pte_swp_mksoft_dirty(swp_pte);
> + if (pte_uffd_wp(pteval))
> + swp_pte = pte_swp_mkuffd_wp(swp_pte);
> set_pte_at(mm, address, pvmw.pte, swp_pte);
> /*
> * No need to invalidate here it will synchronize on
> @@ -1627,6 +1631,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> swp_pte = swp_entry_to_pte(entry);
> if (pte_soft_dirty(pteval))
> swp_pte = pte_swp_mksoft_dirty(swp_pte);
> + if (pte_uffd_wp(pteval))
> + swp_pte = pte_swp_mkuffd_wp(swp_pte);
> set_pte_at(mm, address, pvmw.pte, swp_pte);
> /* Invalidate as we cleared the pte */
> mmu_notifier_invalidate_range(mm, address,
> --
> 2.17.1
>

--
Sincerely yours,
Mike.