Re: [PATCH v2 12/26] userfaultfd: wp: apply _PAGE_UFFD_WP bit

Mike Rapoport
2019-02-25T18:02:08Z

On Tue, Feb 12, 2019 at 10:56:18AM +0800, Peter Xu wrote:
> Firstly, introduce two new flags MM_CP_UFFD_WP[_RESOLVE] for
> change_protection() when used with uffd-wp and make sure the two new
> flags are exclusively used. Then,
>
> - For MM_CP_UFFD_WP: apply the _PAGE_UFFD_WP bit and remove _PAGE_RW
> when a range of memory is write protected by uffd
>
> - For MM_CP_UFFD_WP_RESOLVE: remove the _PAGE_UFFD_WP bit and recover
> _PAGE_RW when write protection is resolved from userspace
>
> And use this new interface in mwriteprotect_range() to replace the old
> MM_CP_DIRTY_ACCT.
>
> Do this change for both PTEs and huge PMDs. Then we can start to
> identify which PTE/PMD is write protected by general (e.g., COW or soft
> dirty tracking), and which is for userfaultfd-wp.
>
> Since we should keep the _PAGE_UFFD_WP when doing pte_modify(), add it
> into _PAGE_CHG_MASK as well. Meanwhile, since we have this new bit, we
> can be even more strict when detecting uffd-wp page faults in either
> do_wp_page() or wp_huge_pmd().
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

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

> ---
> arch/x86/include/asm/pgtable_types.h | 2 +-
> include/linux/mm.h | 5 +++++
> mm/huge_memory.c | 14 +++++++++++++-
> mm/memory.c | 4 ++--
> mm/mprotect.c | 12 ++++++++++++
> mm/userfaultfd.c | 8 ++++++--
> 6 files changed, 39 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 8cebcff91e57..dd9c6295d610 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -133,7 +133,7 @@
> */
> #define _PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \
> _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY | \
> - _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
> + _PAGE_SOFT_DIRTY | _PAGE_DEVMAP | _PAGE_UFFD_WP)
> #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
>
> /*
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 9fe3b0066324..f38fbe9c8bc9 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1657,6 +1657,11 @@ extern unsigned long move_page_tables(struct vm_area_struct *vma,
> #define MM_CP_DIRTY_ACCT (1UL << 0)
> /* Whether this protection change is for NUMA hints */
> #define MM_CP_PROT_NUMA (1UL << 1)
> +/* Whether this change is for write protecting */
> +#define MM_CP_UFFD_WP (1UL << 2) /* do wp */
> +#define MM_CP_UFFD_WP_RESOLVE (1UL << 3) /* Resolve wp */
> +#define MM_CP_UFFD_WP_ALL (MM_CP_UFFD_WP | \
> + MM_CP_UFFD_WP_RESOLVE)
>
> extern unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
> unsigned long end, pgprot_t newprot,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8d65b0f041f9..817335b443c2 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1868,6 +1868,8 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> bool preserve_write;
> int ret;
> bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
> + bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
> + bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
>
> ptl = __pmd_trans_huge_lock(pmd, vma);
> if (!ptl)
> @@ -1934,6 +1936,13 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> entry = pmd_modify(entry, newprot);
> if (preserve_write)
> entry = pmd_mk_savedwrite(entry);
> + if (uffd_wp) {
> + entry = pmd_wrprotect(entry);
> + entry = pmd_mkuffd_wp(entry);
> + } else if (uffd_wp_resolve) {
> + entry = pmd_mkwrite(entry);
> + entry = pmd_clear_uffd_wp(entry);
> + }
> ret = HPAGE_PMD_NR;
> set_pmd_at(mm, addr, pmd, entry);
> BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
> @@ -2083,7 +2092,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> struct page *page;
> pgtable_t pgtable;
> pmd_t old_pmd, _pmd;
> - bool young, write, soft_dirty, pmd_migration = false;
> + bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
> unsigned long addr;
> int i;
>
> @@ -2165,6 +2174,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> write = pmd_write(old_pmd);
> young = pmd_young(old_pmd);
> soft_dirty = pmd_soft_dirty(old_pmd);
> + uffd_wp = pmd_uffd_wp(old_pmd);
> }
> VM_BUG_ON_PAGE(!page_count(page), page);
> page_ref_add(page, HPAGE_PMD_NR - 1);
> @@ -2198,6 +2208,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> entry = pte_mkold(entry);
> if (soft_dirty)
> entry = pte_mksoft_dirty(entry);
> + if (uffd_wp)
> + entry = pte_mkuffd_wp(entry);
> }
> pte = pte_offset_map(&_pmd, addr);
> BUG_ON(!pte_none(*pte));
> diff --git a/mm/memory.c b/mm/memory.c
> index 00781c43407b..f8d83ae16eff 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2483,7 +2483,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
> {
> struct vm_area_struct *vma = vmf->vma;
>
> - if (userfaultfd_wp(vma)) {
> + if (userfaultfd_pte_wp(vma, *vmf->pte)) {
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> return handle_userfault(vmf, VM_UFFD_WP);
> }
> @@ -3692,7 +3692,7 @@ static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf)
> static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf, pmd_t orig_pmd)
> {
> if (vma_is_anonymous(vmf->vma)) {
> - if (userfaultfd_wp(vmf->vma))
> + if (userfaultfd_huge_pmd_wp(vmf->vma, orig_pmd))
> return handle_userfault(vmf, VM_UFFD_WP);
> return do_huge_pmd_wp_page(vmf, orig_pmd);
> }
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index a6ba448c8565..9d4433044c21 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -46,6 +46,8 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> int target_node = NUMA_NO_NODE;
> bool dirty_accountable = cp_flags & MM_CP_DIRTY_ACCT;
> bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
> + bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
> + bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
>
> /*
> * Can be called with only the mmap_sem for reading by
> @@ -117,6 +119,14 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> if (preserve_write)
> ptent = pte_mk_savedwrite(ptent);
>
> + if (uffd_wp) {
> + ptent = pte_wrprotect(ptent);
> + ptent = pte_mkuffd_wp(ptent);
> + } else if (uffd_wp_resolve) {
> + ptent = pte_mkwrite(ptent);
> + ptent = pte_clear_uffd_wp(ptent);
> + }
> +
> /* Avoid taking write faults for known dirty pages */
> if (dirty_accountable && pte_dirty(ptent) &&
> (pte_soft_dirty(ptent) ||
> @@ -301,6 +311,8 @@ unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
> {
> unsigned long pages;
>
> + BUG_ON((cp_flags & MM_CP_UFFD_WP_ALL) == MM_CP_UFFD_WP_ALL);
> +
> if (is_vm_hugetlb_page(vma))
> pages = hugetlb_change_protection(vma, start, end, newprot);
> else
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 73a208c5c1e7..80bcd642911d 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -73,8 +73,12 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
> goto out_release;
>
> _dst_pte = pte_mkdirty(mk_pte(page, dst_vma->vm_page_prot));
> - if (dst_vma->vm_flags & VM_WRITE && !wp_copy)
> - _dst_pte = pte_mkwrite(_dst_pte);
> + if (dst_vma->vm_flags & VM_WRITE) {
> + if (wp_copy)
> + _dst_pte = pte_mkuffd_wp(_dst_pte);
> + else
> + _dst_pte = pte_mkwrite(_dst_pte);
> + }
>
> dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
> if (dst_vma->vm_file) {
> --
> 2.17.1
>

--
Sincerely yours,
Mike.