Re: [PATCH v9 11/24] mm: Cache some VMA fields in the vm_fault structure

[David Rientjes <rientjes@google.com>]

On Tue, 13 Mar 2018, Laurent Dufour wrote:

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ef6ef0627090..dfa81a638b7c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -359,6 +359,12 @@ struct vm_fault {
>  					 * page table to avoid allocation from
>  					 * atomic context.
>  					 */
> +	/*
> +	 * These entries are required when handling speculative page fault.
> +	 * This way the page handling is done using consistent field values.
> +	 */
> +	unsigned long vma_flags;
> +	pgprot_t vma_page_prot;
>  };
>  
>  /* page entry size for vm->huge_fault() */
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 446427cafa19..f71db2b42b30 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3717,6 +3717,8 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  				.vma = vma,
>  				.address = address,
>  				.flags = flags,
> +				.vma_flags = vma->vm_flags,
> +				.vma_page_prot = vma->vm_page_prot,
>  				/*
>  				 * Hard to debug if it ends up being
>  				 * used by a callee that assumes
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 32314e9e48dd..a946d5306160 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -882,6 +882,8 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
>  		.flags = FAULT_FLAG_ALLOW_RETRY,
>  		.pmd = pmd,
>  		.pgoff = linear_page_index(vma, address),
> +		.vma_flags = vma->vm_flags,
> +		.vma_page_prot = vma->vm_page_prot,
>  	};
>  
>  	/* we only decide to swapin, if there is enough young ptes */
> diff --git a/mm/memory.c b/mm/memory.c
> index 0200340ef089..46fe92b93682 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2615,7 +2615,7 @@ static int wp_page_copy(struct vm_fault *vmf)
>  		 * Don't let another task, with possibly unlocked vma,
>  		 * keep the mlocked page.
>  		 */
> -		if (page_copied && (vma->vm_flags & VM_LOCKED)) {
> +		if (page_copied && (vmf->vma_flags & VM_LOCKED)) {
>  			lock_page(old_page);	/* LRU manipulation */
>  			if (PageMlocked(old_page))
>  				munlock_vma_page(old_page);

Doesn't wp_page_copy() also need to pass this to anon_vma_prepare() so 
that find_mergeable_anon_vma() works correctly?

> @@ -2649,7 +2649,7 @@ static int wp_page_copy(struct vm_fault *vmf)
>   */
>  int finish_mkwrite_fault(struct vm_fault *vmf)
>  {
> -	WARN_ON_ONCE(!(vmf->vma->vm_flags & VM_SHARED));
> +	WARN_ON_ONCE(!(vmf->vma_flags & VM_SHARED));
>  	if (!pte_map_lock(vmf))
>  		return VM_FAULT_RETRY;
>  	/*
> @@ -2751,7 +2751,7 @@ static int do_wp_page(struct vm_fault *vmf)
>  		 * We should not cow pages in a shared writeable mapping.
>  		 * Just mark the pages writable and/or call ops->pfn_mkwrite.
>  		 */
> -		if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
> +		if ((vmf->vma_flags & (VM_WRITE|VM_SHARED)) ==
>  				     (VM_WRITE|VM_SHARED))
>  			return wp_pfn_shared(vmf);
>  
> @@ -2798,7 +2798,7 @@ static int do_wp_page(struct vm_fault *vmf)
>  			return VM_FAULT_WRITE;
>  		}
>  		unlock_page(vmf->page);
> -	} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
> +	} else if (unlikely((vmf->vma_flags & (VM_WRITE|VM_SHARED)) ==
>  					(VM_WRITE|VM_SHARED))) {
>  		return wp_page_shared(vmf);
>  	}
> @@ -3067,7 +3067,7 @@ int 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);
> +	pte = mk_pte(page, vmf->vma_page_prot);
>  	if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) {
>  		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
>  		vmf->flags &= ~FAULT_FLAG_WRITE;
> @@ -3093,7 +3093,7 @@ int do_swap_page(struct vm_fault *vmf)
>  
>  	swap_free(entry);
>  	if (mem_cgroup_swap_full(page) ||
> -	    (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
> +	    (vmf->vma_flags & VM_LOCKED) || PageMlocked(page))
>  		try_to_free_swap(page);
>  	unlock_page(page);
>  	if (page != swapcache && swapcache) {
> @@ -3150,7 +3150,7 @@ static int do_anonymous_page(struct vm_fault *vmf)
>  	pte_t entry;
>  
>  	/* File mapping without ->vm_ops ? */
> -	if (vma->vm_flags & VM_SHARED)
> +	if (vmf->vma_flags & VM_SHARED)
>  		return VM_FAULT_SIGBUS;
>  
>  	/*
> @@ -3174,7 +3174,7 @@ static int do_anonymous_page(struct vm_fault *vmf)
>  	if (!(vmf->flags & FAULT_FLAG_WRITE) &&
>  			!mm_forbids_zeropage(vma->vm_mm)) {
>  		entry = pte_mkspecial(pfn_pte(my_zero_pfn(vmf->address),
> -						vma->vm_page_prot));
> +						vmf->vma_page_prot));
>  		if (!pte_map_lock(vmf))
>  			return VM_FAULT_RETRY;
>  		if (!pte_none(*vmf->pte))
> @@ -3207,8 +3207,8 @@ static int do_anonymous_page(struct vm_fault *vmf)
>  	 */
>  	__SetPageUptodate(page);
>  
> -	entry = mk_pte(page, vma->vm_page_prot);
> -	if (vma->vm_flags & VM_WRITE)
> +	entry = mk_pte(page, vmf->vma_page_prot);
> +	if (vmf->vma_flags & VM_WRITE)
>  		entry = pte_mkwrite(pte_mkdirty(entry));
>  
>  	if (!pte_map_lock(vmf)) {
> @@ -3404,7 +3404,7 @@ static int do_set_pmd(struct vm_fault *vmf, struct page *page)
>  	for (i = 0; i < HPAGE_PMD_NR; i++)
>  		flush_icache_page(vma, page + i);
>  
> -	entry = mk_huge_pmd(page, vma->vm_page_prot);
> +	entry = mk_huge_pmd(page, vmf->vma_page_prot);
>  	if (write)
>  		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
>  
> @@ -3478,11 +3478,11 @@ int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
>  		return VM_FAULT_NOPAGE;
>  
>  	flush_icache_page(vma, page);
> -	entry = mk_pte(page, vma->vm_page_prot);
> +	entry = mk_pte(page, vmf->vma_page_prot);
>  	if (write)
>  		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>  	/* copy-on-write page */
> -	if (write && !(vma->vm_flags & VM_SHARED)) {
> +	if (write && !(vmf->vma_flags & VM_SHARED)) {
>  		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
>  		page_add_new_anon_rmap(page, vma, vmf->address, false);
>  		mem_cgroup_commit_charge(page, memcg, false, false);
> @@ -3521,7 +3521,7 @@ int finish_fault(struct vm_fault *vmf)
>  
>  	/* Did we COW the page? */
>  	if ((vmf->flags & FAULT_FLAG_WRITE) &&
> -	    !(vmf->vma->vm_flags & VM_SHARED))
> +	    !(vmf->vma_flags & VM_SHARED))
>  		page = vmf->cow_page;
>  	else
>  		page = vmf->page;
> @@ -3775,7 +3775,7 @@ static int do_fault(struct vm_fault *vmf)
>  		ret = VM_FAULT_SIGBUS;
>  	else if (!(vmf->flags & FAULT_FLAG_WRITE))
>  		ret = do_read_fault(vmf);
> -	else if (!(vma->vm_flags & VM_SHARED))
> +	else if (!(vmf->vma_flags & VM_SHARED))
>  		ret = do_cow_fault(vmf);
>  	else
>  		ret = do_shared_fault(vmf);
> @@ -3832,7 +3832,7 @@ static int do_numa_page(struct vm_fault *vmf)
>  	 * accessible ptes, some can allow access by kernel mode.
>  	 */
>  	pte = ptep_modify_prot_start(vma->vm_mm, vmf->address, vmf->pte);
> -	pte = pte_modify(pte, vma->vm_page_prot);
> +	pte = pte_modify(pte, vmf->vma_page_prot);
>  	pte = pte_mkyoung(pte);
>  	if (was_writable)
>  		pte = pte_mkwrite(pte);
> @@ -3866,7 +3866,7 @@ static int do_numa_page(struct vm_fault *vmf)
>  	 * Flag if the page is shared between multiple address spaces. This
>  	 * is later used when determining whether to group tasks together
>  	 */
> -	if (page_mapcount(page) > 1 && (vma->vm_flags & VM_SHARED))
> +	if (page_mapcount(page) > 1 && (vmf->vma_flags & VM_SHARED))
>  		flags |= TNF_SHARED;
>  
>  	last_cpupid = page_cpupid_last(page);
> @@ -3911,7 +3911,7 @@ static inline int wp_huge_pmd(struct vm_fault *vmf, pmd_t orig_pmd)
>  		return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD);
>  
>  	/* COW handled on pte level: split pmd */
> -	VM_BUG_ON_VMA(vmf->vma->vm_flags & VM_SHARED, vmf->vma);
> +	VM_BUG_ON_VMA(vmf->vma_flags & VM_SHARED, vmf->vma);
>  	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
>  
>  	return VM_FAULT_FALLBACK;
> @@ -4058,6 +4058,8 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  		.flags = flags,
>  		.pgoff = linear_page_index(vma, address),
>  		.gfp_mask = __get_fault_gfp_mask(vma),
> +		.vma_flags = vma->vm_flags,
> +		.vma_page_prot = vma->vm_page_prot,
>  	};
>  	unsigned int dirty = flags & FAULT_FLAG_WRITE;
>  	struct mm_struct *mm = vma->vm_mm;

Don't you also need to do this?

diff --git a/include/linux/mm.h b/include/linux/mm.h
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -694,9 +694,9 @@ void free_compound_page(struct page *page);
  * pte_mkwrite.  But get_user_pages can cause write faults for mappings
  * that do not have writing enabled, when used by access_process_vm.
  */
-static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
+static inline pte_t maybe_mkwrite(pte_t pte, unsigned long vma_flags)
 {
-	if (likely(vma->vm_flags & VM_WRITE))
+	if (likely(vma_flags & VM_WRITE))
 		pte = pte_mkwrite(pte);
 	return pte;
 }
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1195,8 +1195,8 @@ static int do_huge_pmd_wp_page_fallback(struct vm_fault *vmf, pmd_t orig_pmd,
 
 	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 		pte_t entry;
-		entry = mk_pte(pages[i], vma->vm_page_prot);
-		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		entry = mk_pte(pages[i], vmf->vma_page_prot);
+		entry = maybe_mkwrite(pte_mkdirty(entry), vmf->vma_flags);
 		memcg = (void *)page_private(pages[i]);
 		set_page_private(pages[i], 0);
 		page_add_new_anon_rmap(pages[i], vmf->vma, haddr, false);
@@ -2169,7 +2169,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 				entry = pte_swp_mksoft_dirty(entry);
 		} else {
 			entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
-			entry = maybe_mkwrite(entry, vma);
+			entry = maybe_mkwrite(entry, vma->vm_flags);
 			if (!write)
 				entry = pte_wrprotect(entry);
 			if (!young)
diff --git a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1826,7 +1826,7 @@ static int insert_pfn(struct vm_area_struct *vma, unsigned long addr,
 out_mkwrite:
 	if (mkwrite) {
 		entry = pte_mkyoung(entry);
-		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma->vm_flags);
 	}
 
 	set_pte_at(mm, addr, pte, entry);
@@ -2472,7 +2472,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
 
 	flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
 	entry = pte_mkyoung(vmf->orig_pte);
-	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	entry = maybe_mkwrite(pte_mkdirty(entry), vmf->vma_flags);
 	if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
 		update_mmu_cache(vma, vmf->address, vmf->pte);
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
@@ -2549,8 +2549,8 @@ static int wp_page_copy(struct vm_fault *vmf)
 			inc_mm_counter_fast(mm, MM_ANONPAGES);
 		}
 		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
-		entry = mk_pte(new_page, vma->vm_page_prot);
-		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		entry = mk_pte(new_page, vmf->vma_page_prot);
+		entry = maybe_mkwrite(pte_mkdirty(entry), vmf->vma_flags);
 		/*
 		 * Clear the pte entry and flush it first, before updating the
 		 * pte with the new entry. This will avoid a race condition
@@ -3069,7 +3069,7 @@ int do_swap_page(struct vm_fault *vmf)
 	dec_mm_counter_fast(vma->vm_mm, MM_SWAPENTS);
 	pte = mk_pte(page, vmf->vma_page_prot);
 	if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) {
-		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
+		pte = maybe_mkwrite(pte_mkdirty(pte), vmf->vm_flags);
 		vmf->flags &= ~FAULT_FLAG_WRITE;
 		ret |= VM_FAULT_WRITE;
 		exclusive = RMAP_EXCLUSIVE;
@@ -3481,7 +3481,7 @@ int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
 	flush_icache_page(vma, page);
 	entry = mk_pte(page, vmf->vma_page_prot);
 	if (write)
-		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		entry = maybe_mkwrite(pte_mkdirty(entry), vmf->vm_flags);
 	/* copy-on-write page */
 	if (write && !(vmf->vma_flags & VM_SHARED)) {
 		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
diff --git a/mm/migrate.c b/mm/migrate.c
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -240,7 +240,7 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
 		 */
 		entry = pte_to_swp_entry(*pvmw.pte);
 		if (is_write_migration_entry(entry))
-			pte = maybe_mkwrite(pte, vma);
+			pte = maybe_mkwrite(pte, vma->vm_flags);
 
 		if (unlikely(is_zone_device_page(new))) {
 			if (is_device_private_page(new)) {