When dealing with speculative page fault handler, we may race with VMA
being split or merged. In this case the vma->vm_start and vm->vm_end
fields may not match the address the page fault is occurring.
This can only happens when the VMA is split but in that case, the
anon_vma pointer of the new VMA will be the same as the original one,
because in __split_vma the new->anon_vma is set to src->anon_vma when
*new = *vma.
So even if the VMA boundaries are not correct, the anon_vma pointer is
still valid.
If the VMA has been merged, then the VMA in which it has been merged
must have the same anon_vma pointer otherwise the merge can't be done.
So in all the case we know that the anon_vma is valid, since we have
checked before starting the speculative page fault that the anon_vma
pointer is valid for this VMA and since there is an anon_vma this
means that at one time a page has been backed and that before the VMA
is cleaned, the page table lock would have to be grab to clean the
PTE, and the anon_vma field is checked once the PTE is locked.
This patch introduce a new __page_add_new_anon_rmap() service which
doesn't check for the VMA boundaries, and create a new inline one
which do the check.
When called from a page fault handler, if this is not a speculative one,
there is a guarantee that vm_start and vm_end match the faulting address,
so this check is useless. In the context of the speculative page fault
handler, this check may be wrong but anon_vma is still valid as explained
above.
Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
---
include/linux/rmap.h | 12 ++++++++++--
mm/memory.c | 8 ++++----
mm/rmap.c | 5 ++---
3 files changed, 16 insertions(+), 9 deletions(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 733d3d8181e2..d91be69c1c60 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -173,8 +173,16 @@ void page_add_anon_rmap(struct page *, struct vm_area_struct *,
unsigned long, bool);
void do_page_add_anon_rmap(struct page *, struct vm_area_struct *,
unsigned long, int);
-void page_add_new_anon_rmap(struct page *, struct vm_area_struct *,
- unsigned long, bool);
+void __page_add_new_anon_rmap(struct page *, struct vm_area_struct *,
+ unsigned long, bool);
+static inline void page_add_new_anon_rmap(struct page *page,
+ struct vm_area_struct *vma,
+ unsigned long address, bool compound)
+{
+ VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
+ __page_add_new_anon_rmap(page, vma, address, compound);
+}
+
void page_add_file_rmap(struct page *, bool);
void page_remove_rmap(struct page *, bool);
diff --git a/mm/memory.c b/mm/memory.c
index 4ad4f0a6f652..3705ff3e04d5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2551,7 +2551,7 @@ static int wp_page_copy(struct vm_fault *vmf)
* thread doing COW.
*/
ptep_clear_flush_notify(vma, vmf->address, vmf->pte);
- page_add_new_anon_rmap(new_page, vma, vmf->address, false);
+ __page_add_new_anon_rmap(new_page, vma, vmf->address, false);
mem_cgroup_commit_charge(new_page, memcg, false, false);
__lru_cache_add_active_or_unevictable(new_page, vmf->vma_flags);
/*
@@ -3065,7 +3065,7 @@ int do_swap_page(struct vm_fault *vmf)
/* ksm created a completely new copy */
if (unlikely(page != swapcache && swapcache)) {
- page_add_new_anon_rmap(page, vma, vmf->address, false);
+ __page_add_new_anon_rmap(page, vma, vmf->address, false);
mem_cgroup_commit_charge(page, memcg, false, false);
__lru_cache_add_active_or_unevictable(page, vmf->vma_flags);
} else {
@@ -3215,7 +3215,7 @@ static int do_anonymous_page(struct vm_fault *vmf)
}
inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
- page_add_new_anon_rmap(page, vma, vmf->address, false);
+ __page_add_new_anon_rmap(page, vma, vmf->address, false);
mem_cgroup_commit_charge(page, memcg, false, false);
__lru_cache_add_active_or_unevictable(page, vmf->vma_flags);
setpte:
@@ -3467,7 +3467,7 @@ int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
/* copy-on-write page */
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);
+ __page_add_new_anon_rmap(page, vma, vmf->address, false);
mem_cgroup_commit_charge(page, memcg, false, false);
__lru_cache_add_active_or_unevictable(page, vmf->vma_flags);
} else {
diff --git a/mm/rmap.c b/mm/rmap.c
index 787c07fb37dc..357ea765e795 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1138,7 +1138,7 @@ void do_page_add_anon_rmap(struct page *page,
}
/**
- * page_add_new_anon_rmap - add pte mapping to a new anonymous page
+ * __page_add_new_anon_rmap - add pte mapping to a new anonymous page
* @page: the page to add the mapping to
* @vma: the vm area in which the mapping is added
* @address: the user virtual address mapped
@@ -1148,12 +1148,11 @@ void do_page_add_anon_rmap(struct page *page,
* This means the inc-and-test can be bypassed.
* Page does not have to be locked.
*/
-void page_add_new_anon_rmap(struct page *page,
+void __page_add_new_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address, bool compound)
{
int nr = compound ? hpage_nr_pages(page) : 1;
- VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
__SetPageSwapBacked(page);
if (compound) {
VM_BUG_ON_PAGE(!PageTransHuge(page), page);
--
2.7.4
--
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