--- v1
+++ v2
@@ -1,23 +1,131 @@
-Add new software events to count succeeded and failed speculative page
-faults.
+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@linux.vnet.ibm.com>
---
- include/uapi/linux/perf_event.h | 2 ++
- 1 file changed, 2 insertions(+)
+ include/linux/rmap.h | 12 ++++++++++--
+ mm/memory.c | 8 ++++----
+ mm/rmap.c | 5 ++---
+ 3 files changed, 16 insertions(+), 9 deletions(-)
-diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
-index b1c0b187acfe..fbfb03dff334 100644
---- a/include/uapi/linux/perf_event.h
-+++ b/include/uapi/linux/perf_event.h
-@@ -111,6 +111,8 @@ enum perf_sw_ids {
- PERF_COUNT_SW_EMULATION_FAULTS = 8,
- PERF_COUNT_SW_DUMMY = 9,
- PERF_COUNT_SW_BPF_OUTPUT = 10,
-+ PERF_COUNT_SW_SPF_DONE = 11,
-+ PERF_COUNT_SW_SPF_FAILED = 12,
+diff --git a/include/linux/rmap.h b/include/linux/rmap.h
+index 43ef2c30cb0f..f5cd4dbc78b0 100644
+--- a/include/linux/rmap.h
++++ b/include/linux/rmap.h
+@@ -170,8 +170,16 @@ 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);
- PERF_COUNT_SW_MAX, /* non-ABI */
- };
+diff --git a/mm/memory.c b/mm/memory.c
+index 9f9e5bb7a556..51bc8315281e 100644
+--- a/mm/memory.c
++++ b/mm/memory.c
+@@ -2376,7 +2376,7 @@ 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);
+ /*
+@@ -2847,7 +2847,7 @@ int do_swap_page(struct vm_fault *vmf)
+ mem_cgroup_commit_charge(page, memcg, true, false);
+ activate_page(page);
+ } else { /* ksm created a completely new copy */
+- 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);
+ }
+@@ -2985,7 +2985,7 @@ 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:
+@@ -3237,7 +3237,7 @@ 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 c1286d47aa1f..0c9f8ded669a 100644
+--- a/mm/rmap.c
++++ b/mm/rmap.c
+@@ -1122,7 +1122,7 @@ 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
+@@ -1132,12 +1132,11 @@ 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