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 <[email protected]>
Few comments but still: Reviewed-by: Jérôme Glisse <[email protected]> > --- > 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) This chunk needs to be in the earlier arch specific patch. [...] > 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 [...] > @@ -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)); Reading that code and i thought i would be nice if we could define a pte_mask that we can or instead of all those if () entry |= ... but that is just some dumb optimization and does not have any bearing on the present patch. Just wanted to say that outloud. > 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); Don't you want to abort and return here if both flags are set ? [...]
