[PATCH v11 13/26] mm: cache some VMA fields in the vm_fault structure

From: Laurent Dufour
Date: Thu May 17 2018 - 06:13:37 EST

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When handling speculative page fault, the vma->vm_flags and
vma->vm_page_prot fields are read once the page table lock is released. So
there is no more guarantee that these fields would not change in our back.
They will be saved in the vm_fault structure before the VMA is checked for
changes.

In the detail, when we deal with a speculative page fault, the mmap_sem is
not taken, so parallel VMA's changes can occurred. When a VMA change is
done which will impact the page fault processing, we assumed that the VMA
sequence counter will be changed. In the page fault processing, at the
time the PTE is locked, we checked the VMA sequence counter to detect
changes done in our back. If no change is detected we can continue further.
But this doesn't prevent the VMA to not be changed in our back while the
PTE is locked. So VMA's fields which are used while the PTE is locked must
be saved to ensure that we are using *static* values. This is important
since the PTE changes will be made on regards to these VMA fields and they
need to be consistent. This concerns the vma->vm_flags and
vma->vm_page_prot VMA fields.

This patch also set the fields in hugetlb_no_page() and
__collapse_huge_page_swapin even if it is not need for the callee.

Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 10 ++++++++--
mm/huge_memory.c | 6 +++---
mm/hugetlb.c | 2 ++
mm/khugepaged.c | 2 ++
mm/memory.c | 50 ++++++++++++++++++++++++++------------------------
mm/migrate.c | 2 +-
6 files changed, 42 insertions(+), 30 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3f8b2ce0ef7c..f385d721867d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -373,6 +373,12 @@ 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() */
@@ -693,9 +699,9 @@ 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
index 323acdd14e6e..6bf5420cc62e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1194,8 +1194,8 @@ 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);
@@ -2168,7 +2168,7 @@ 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/hugetlb.c b/mm/hugetlb.c
index 129088710510..d7764b6568f5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3718,6 +3718,8 @@ 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 0b28af4b950d..2b02a9f9589e 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -887,6 +887,8 @@ 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 d0b5f14cfe69..9dc455ae550c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1822,7 +1822,7 @@ 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);
@@ -2482,7 +2482,7 @@ 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);
@@ -2558,8 +2558,8 @@ 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
@@ -2624,7 +2624,7 @@ 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);
@@ -2660,7 +2660,7 @@ 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;
/*
@@ -2762,7 +2762,7 @@ 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);

@@ -2809,7 +2809,7 @@ 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);
}
@@ -3088,9 +3088,9 @@ 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);
+ pte = maybe_mkwrite(pte_mkdirty(pte), vmf->vma_flags);
vmf->flags &= ~FAULT_FLAG_WRITE;
ret |= VM_FAULT_WRITE;
exclusive = RMAP_EXCLUSIVE;
@@ -3115,7 +3115,7 @@ 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) {
@@ -3173,7 +3173,7 @@ 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;

/*
@@ -3197,7 +3197,7 @@ 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))
@@ -3230,8 +3230,8 @@ 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)) {
@@ -3428,7 +3428,7 @@ 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);

@@ -3502,11 +3502,11 @@ 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);
+ entry = maybe_mkwrite(pte_mkdirty(entry), vmf->vma_flags);
/* 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);
@@ -3545,7 +3545,7 @@ 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;
@@ -3799,7 +3799,7 @@ 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);
@@ -3856,7 +3856,7 @@ 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);
@@ -3890,7 +3890,7 @@ 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);
@@ -3935,7 +3935,7 @@ 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;
@@ -4082,6 +4082,8 @@ 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;
diff --git a/mm/migrate.c b/mm/migrate.c
index 8c0af0f7cab1..ae3d0faf72cb 100644
--- 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)) {
--
2.7.4

Next message: Laurent Dufour: "[PATCH v11 15/26] mm: introduce __lru_cache_add_active_or_unevictable"
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